Semiconductor Device and Display Device

ABSTRACT

If misalignment in a line width direction of an electrode (pad) of a connection terminal is caused in attachment of a substrate and an FPC, a connection area of the FPC terminal and the connection terminal becomes smaller and contact resistance is increased. In particular, an increase in contact resistance of the connection terminal to which a power supply potential serving as a power source is inputted is a cause of defective display. In view of the above, an object of the present invention is to decrease the resistance of a power supply line, to suppress a voltage drop in the power supply line, and to prevent defective display. A connection terminal portion includes a plurality of connection terminals. The plurality of connection terminals is provided with a plurality of connection pads which is part of the connection terminal. The plurality of connection pads includes a first connection pad and a second connection pad having a line width different from that of the first connection pad. Pitches between the plurality of connection pads are equal to each other.

BACKGROUND OF THE INVENTION

1. Field the Invention

The present invention relates to a semiconductor device including aconnection terminal. In particular, the invention relates to a structureof a connection terminal of a display device including a pixel portionwhere pixels are arranged in matrix, and to a connection structurebetween an external terminal and a connection terminal of a displaydevice.

2. Description of the Related Art

A display device may have a structure in which a flexible printedcircuit is conductively connected to a display panel and a signal andpower are supplied through the flexible printed circuit to the displaypanel.

For example, the display panel includes a pixel portion and a peripheraldriver circuit for driving the pixel portion over a substrate, and thesubstrate is attached to an opposite substrate with a sealant in asealing region. Then, at least the pixel portion is sealed with thesubstrate, the opposite substrate, and the sealant.

The substrate includes a region which is not overlapped with theopposite substrate, and a connection terminal portion is formed in thatregion. In the connection terminal portion, electrodes (connection pads)are arranged in stripes. Each of the electrodes is connected to a wirewhich is formed to extend outward from inside the sealing region.

As for the display panel, in the connection terminal portion, theelectrode (connection pad) of a connection terminal is electricallyconnected to an electrode (FPC pad) of a flexible printed circuitterminal with an anisotropic conductive film or the like bythermocompression bonding.

Then, the signal and power supplied from the flexible printed circuitare supplied to a circuit over the substrate through each connectionterminal and wire.

Here, a large amount of current flows through a power supply line (powersupply path) including wires for supplying a power supply potentialserving as a power source of the circuit over the substrate, aconnection portion between the wires, a connection portion between theFPC terminal and the connection terminal over the substrate, and thelike in order to operate the pixel, the peripheral driver circuit, andthe like.

Therefore, there is a significant voltage drop in the power supply lineif the resistance of the power supply line is high. Accordingly, thepower supply potential supplied to the pixel and the peripheral drivercircuit becomes lower than a desired power supply potential. As aresult, a power supply potential inputted to the pixel and theperipheral driver circuit is decreased, which causes defective display.

Thus, References 1 and 2 disclose a structure in which power is suppliedthrough a plurality of wires of a flexible printed circuit and wiresconnected to connection terminals to which a power supply potentialserving as a power source of a circuit over a substrate is inputted, areconnected to each other in a sealing region (Reference 1: JapanesePatent Laid-Open No. 2001-109395 and Reference 2: Japanese PatentApplication Laid-Open No. 2001-102169).

However, even according to the above structure, if misalignment in aline width direction of the connection pad is caused in attachment ofthe substrate and the FPC, a connection area between the FPC terminaland the connection terminal becomes smaller and contact resistance isincreased. In particular, an increase in contact resistance of theconnection terminal to which a power supply potential serving as a powersource is inputted is a cause of defective display.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention todecrease the resistance of a power supply line, to suppress a voltagedrop in the power supply line, and to prevent defective display.

The constitution of the present invention is described hereinafter.

A semiconductor device of the present invention includes a connectionterminal portion, and the connection terminal portion includes aplurality of connection terminals. The plurality of connection terminalsare provided with a plurality of connection pads each of which is partof the connection terminal. The plurality of connection pads include afirst connection pad and a second connection pad having a line widthdifferent from that of the first connection pad.

In addition, a semiconductor device of the present invention includes aconnection terminal portion, and the connection terminal portionincludes a plurality of connection terminals. The plurality ofconnection terminals are provided with a plurality of connection padseach of which is part of the connection terminal. The plurality ofconnection pads include a first connection pad and a second connectionpad having a line width different from that of the first connection pad.Pitches between the plurality of connection pads are equal to eachother.

In addition, a semiconductor device of the present invention includes aconnection terminal portion. The connection terminal portion includes aconnection terminal in which a plurality of connection pads having equalline widths are arranged equally spaced, and two or more of theplurality of connection pads are connected with each other with a wireled in the connection terminal portion.

In addition, a semiconductor device of the present invention includes aconnection terminal portion. The connection terminal portion includes aconnection terminal in which a plurality of connection pads having equalline widths are arranged equally spaced, and two or more of theplurality of connection pads are connected to each other with anelectrode in a lower layer through contact holes.

In the semiconductor device of the invention according to the aboveconfiguration, a flexible printed circuit is connected to the connectionterminal portion.

In the semiconductor device of the invention according to the aboveconfiguration, at least one connection terminal in the connectionterminal portion is connected to a plurality of terminals of theflexible printed circuit, and a contact resistance between theconnection terminal and the plurality of terminals of the flexibleprinted circuit is 5Ω or less.

A display device of the present invention includes a pixel portion, aperipheral driver circuit, and a connection terminal portion. Theconnection terminal portion includes a plurality of connectionterminals. The plurality of connection terminals are provided with aplurality of connection pads each of which is part of the connectionterminal. The plurality of connection pads include a first connectionpad and a second connection pad having a line width different from thatof the first connection pad.

In addition, a display device of the present invention includes a pixelportion, a peripheral driver circuit, and a connection terminal portion.The connection terminal portion includes a plurality of connectionterminals. The plurality of connection terminals are provided with aplurality of connection pads each of which is part of the connectionterminal. The plurality of connection pads include a first connectionpad and a second connection pad having a line width different from thatof the first connection pad. Pitches between the plurality of connectionpads are equal to each other.

In addition, a display device of the present invention includes a pixelportion, a peripheral driver circuit, and a connection terminal portion.The connection terminal portion includes a connection terminal in whicha plurality of connection pads having equal line widths are arrangedequally spaced, and two or more of the plurality of connection pads areconnected with each other with a wire led in the connection terminalportion.

In addition, a display device of the present invention includes a pixelportion, a peripheral driver circuit, and a connection terminal portion.The connection terminal portion includes a connection terminal in whicha plurality of connection pads having equal line widths are arrangedequally spaced, and two or more of the plurality of connection pads areconnected to each other with an electrode in a lower layer throughcontact holes.

In the display device of the invention according to the aboveconfiguration, a flexible printed circuit is connected to the connectionterminal portion.

In the display device of the invention according to the aboveconfiguration, at least one connection terminal in the connectionterminal portion is connected to a plurality of terminals of theflexible printed circuit, and a contact resistance between theconnection terminal and the plurality of terminals of the flexibleprinted circuit is 5Ω or less.

In addition, a display device of the present invention includes a pixelportion, a peripheral driver circuit, and a connection terminal portion.The connection terminal portion includes a plurality of connectionterminals. The plurality of connection terminals are provided with aplurality of connection pads each of which is part of the connectionterminal. Pitches between the plurality of connection pads are equal toeach other. The plurality of connection pads include a first connectionpad and a second connection pad having a line width larger than that ofthe first connection pad. A plurality of wires are electricallyconnected to the second connection pad. The plurality of wires areelectrically connected to an opposite electrode of an element.

Note that a switch to be described in the present invention can be ofvarious types, one example of which is an electric switch, a mechanicalswitch, or the like. In other words, any switch that can control currentflow can be used, and various kinds of switches can be used withoutlimitation to a specific switch. For example, the switch may be atransistor, a diode (such as a PN diode, a PIN diode, a Schottky diode,or a diode-connected transistor), or a logic circuit that is acombination thereof. In the case of using a transistor as the switch,the transistor operates as a mere switch. Therefore, the polarity(conductivity type) of the transistor is not particularly limited.However, in the case where less off-current is desired, it is desirableto use a transistor having a polarity with less off-current. As thetransistor with small off-current, a transistor provided with an LDDregion, a transistor having a multi-gate structure, or the like can beused. In addition, it is desirable to use an n-channel transistor in thecase where a transistor to be operated as a switch operates in a statewhere a potential of a source terminal thereof is close to a lowerpotential side power source (such as Vss, GND, or 0V), whereas it isdesirable to use a p-channel transistor in the case where a transistoroperates in a state where a potential of a source terminal thereof isclose to a higher potential side power source (such as Vdd). This isbecause an absolute value of a gate-source voltage can be increased, sothat the transistor easily operates as a switch. Note that the switchmay be of CMOS type using both an n-channel transistor and a p-channeltransistor. If the switch is of CMOS type, it can operate appropriatelyeven in the case where conditions vary, for example, a voltage to beoutputted through the switch (in other words, an input voltage to theswitch) is higher or lower than an output voltage.

Note that in this invention, the phrase “being connected” means the caseof being electrically connected and the case of being directlyconnected. Therefore, in the constitution disclosed in the invention,another element (such as a switch, a transistor, a capacitor, aninductor, a resistor, or a diode) which enables electrical connectionmay be interposed in a predetermined connection. Alternatively,components may be directly connected in the arrangement without anotherelement interposed therebetween. Note that only the case wherecomponents are directly connected without another element enablingelectrical connection interposed therebetween, not including the case ofbeing electrically connected, is referred to as “being directlyconnected”. Note also that the phrase “being electrically connected”means both the case where components are electrically connected and thecase where components are directly connected.

Note that as the transistor, transistors of various types can beemployed in the invention. Therefore, there is no limitation on the kindof applicable transistor. Thus, a thin film transistor (TFT) using anon-single crystal semiconductor film typified by an amorphous siliconfilm or a polycrystalline silicon film, a MOS transistor formed using asemiconductor substrate or an SOI substrate, a junction transistor, abipolar transistor, a transistor using a compound semiconductor such asZnO or a-InGaZnO, a transistor using an organic semiconductor or acarbon nanotube, or another transistor can be used. Note that thenon-single crystal semiconductor film may contain hydrogen or halogen.In addition, the transistor may be located over various kinds ofsubstrates, and the kind of substrate is not limited to a specific one.Therefore, the transistor can be located over, for example, asingle-crystal substrate, an SOI substrate, a glass substrate, a quartzsubstrate, a plastic substrate, a paper substrate, a cellophanesubstrate, a stone substrate, or the like. Further, the transistor maybe formed over a certain substrate, and later, may be transferred to andlocated over another substrate.

Note that in the present invention, it is assumed that a pixel is thesmallest unit of an image. Therefore, in the case of a full colordisplay device including color elements R (red), G (green), and B(blue), it is assumed that a pixel includes a dot of the color elementR, a dot of the color element and a dot of the color element B. Notethat the color element is not limited to three colors, and may be morethan three colors. For example, RGBW (W is white), RGB to which yellow,cyan, or magenta is added, and the like can be used. Note that one pixelmay include a plurality of dots of a certain color element. In thatcase, the plurality of color elements may each have different sizes ofregions that contribute to display. In addition, gradation may beexpressed by individually controlling the plurality of dots of a certaincolor element. This is referred to as an area gray scale method.Alternatively, a viewing angle may be increased by supplying slightlydifferent signals to respective dots of the plurality of dots of acertain color element.

Note that the phrase “pixels are arranged (arrayed) in matrix” includesthe case of stripe arrangement in a so-called grid of a combination ofvertical stripes and lateral stripes. It also includes the case ofso-called delta arrangement of dots of three color elements (forexample, RGB) in the case of performing full color display with thethree color elements. Furthermore, it also includes the case of Bayerarrangement. Note that the color element is not limited to three colors,and may be more than three colors. For example, RGBW (W is white), RGBto which yellow, cyan, or magenta is added, and the like can be used.Furthermore, dots of color elements may each have different sizes oflight emitting regions.

Note that in the invention, the term “semiconductor device” means adevice having a circuit including a semiconductor element (such as atransistor or a diode). In addition, it may also mean a device ingeneral that can operate by utilizing semiconductor characteristics. Theterm “display device” means a device including a display element (suchas a liquid crystal element or a light emitting element). Note that itmay also mean a main body of a display panel in which a plurality ofpixels each including a display element such as a liquid crystal elementor an EL element and a peripheral driver circuit for driving the pixelsare formed over a substrate. Moreover, it may include a device to whicha flexible printed circuit (FPC) or a printed wiring board (PWB) isattached (such as an IC, a resistor, a capacitor, an inductor, or atransistor). Further, it may also include an optical sheet such as apolarizing plate or a retardation film. Furthermore, it may include abacklight (which may include a light conducting plate, a prism sheet, adiffusion sheet, a reflection sheet, or a light source (such as an LEDor a cold cathode tube)).

Defective display can be prevented by decreasing the resistance of apower supply line and suppressing a voltage drop in the power supplyline.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are a diagram showing a display panel of the presentinvention and a diagram explaining a connection terminal portion,respectively.

FIG. 2 is a schematic diagram of a display device of the presentinvention.

FIG. 3 is a schematic diagram of a display device of the presentinvention.

FIGS. 4A to 4C are diagrams explaining a connection terminal portion.

FIGS. 5A and 5B are diagrams explaining a connection terminal portion.

FIGS. 6A to 6F are diagrams explaining a connection terminal portion.

FIG. 7 is a schematic diagram of a display device of the presentinvention.

FIG. 8 is a diagram showing a display panel of the present invention.

FIG. 9 is a schematic diagram of a display device of the presentinvention.

FIG. 10 is a diagram explaining a connection terminal portion.

FIG. 11 is a diagram explaining a connection terminal portion.

FIG. 12 is a diagram explaining a connection terminal portion.

FIG. 13 is a schematic diagram of a display device of the presentinvention.

FIG. 14 is a schematic diagram of a display device of the presentinvention.

FIG. 15 is a schematic diagram of a display device of the presentinvention.

FIG. 16 is a schematic diagram of a display device of the presentinvention.

FIG. 17 is a schematic diagram of a display device of the presentinvention.

FIG. 18 is a schematic diagram of a display device of the presentinvention.

FIG. 19 is a schematic diagram of a display device of the presentinvention.

FIG. 20 is a schematic diagram of a display device of the presentinvention.

FIG. 21 is a schematic diagram of a display device of the presentinvention.

FIG. 22 is a schematic diagram of a display device of the presentinvention.

FIG. 23 is a schematic diagram of a display device of the presentinvention.

FIG. 24 is a schematic diagram of a display device of the presentinvention.

FIG. 25 is a schematic diagram of a display device of the presentinvention.

FIG. 26 is a schematic diagram of a display device of the presentinvention.

FIG. 27 is a schematic diagram of a display device of the presentinvention.

FIG. 28 is a schematic diagram of a display device of the presentinvention.

FIG. 29 is a schematic diagram of a display device of the presentinvention.

FIG. 30 is a schematic diagram of a display device of the presentinvention.

FIG. 31 is a schematic diagram of a display device of the presentinvention.

FIG. 32 is a schematic diagram of a display device of the presentinvention.

FIG. 33 is a schematic diagram of a display device of the presentinvention.

FIG. 34 is a schematic diagram of a display device of the presentinvention.

FIGS. 35A to 35C are diagrams explaining a connection terminal portion.

FIG. 36 is a diagram explaining a connection terminal portion.

FIG. 37 is a diagram explaining a connection terminal portion.

FIG. 38 is a diagram explaining a connection terminal portion.

FIGS. 39A and 39B are diagrams explaining a connection terminal portion.

FIG. 40 is a schematic diagram of a display device of the presentinvention.

FIG. 41 is a schematic diagram of a display device of the presentinvention.

FIG. 42 is a diagram explaining a signal line driver circuit.

FIGS. 43A to 43C are diagrams explaining a current source circuit.

FIG. 44 is a diagram explaining a connection terminal portion.

FIG. 45 is a diagram explaining a connection terminal portion.

FIG. 46 is a diagram explaining a connection terminal portion.

FIG. 47 is a diagram explaining a connection terminal portion.

FIG. 48 is a diagram explaining a connection terminal portion.

FIG. 49 is a diagram explaining a connection terminal portion.

FIG. 50 is a diagram explaining a connection terminal portion.

FIG. 51 is a diagram explaining a connection terminal portion.

FIGS. 52A and 52B are cross-sectional views of a display device of thepresent invention.

FIGS. 53A and 53B are cross-sectional views of a display device of thepresent invention.

FIGS. 54A and 54B are cross-sectional views of a display device of thepresent invention.

FIGS. 55A and 55B are cross-sectional views of a display device of thepresent invention.

FIGS. 56A and 56B are cross-sectional views of a display device of thepresent invention.

FIGS. 57A and 57B are cross-sectional views of a display device of thepresent invention.

FIGS. 58A and 58B are cross-sectional views of a display device of thepresent invention.

FIGS. 59A and 59B are cross-sectional views of a display device of thepresent invention.

FIGS. 60A and 60B are cross-sectional views of a display device of thepresent invention.

FIG. 61 is a diagram explaining a connection terminal portion.

FIG. 62 shows an example of an EL module.

FIG. 63 is a block diagram showing a main structure of an EL televisionreceiver.

FIG. 64 shows an example of a mobile phone to which the presentinvention can be applied.

FIGS. 65A to 65H show an example of an electronic device.

FIGS. 66A and 66B are a schematic diagram showing a structure of adisplay panel of the present invention and a schematic diagram showing astructure of a display panel of the present invention, respectively.

FIG. 67 is a diagram explaining a connection terminal portion.

FIGS. 68A and 68B are diagrams explaining power supply to a shiftregister and a buffer circuit.

FIG. 69 is a diagram showing a display panel of the present invention.

FIG. 70 is a diagram showing a display panel of the present invention.

FIGS. 71A and 71B are diagrams showing a display panel of the presentinvention.

FIGS. 72A and 72B are diagrams showing a light emitting element.

FIGS. 73A to 73C are cross-sectional views of a display device.

FIG. 74 is a cross-sectional view of a display device.

FIG. 75 is a cross-sectional view of a display device.

FIGS. 76A and 76B are diagrams showing a display panel of the presentinvention.

FIG. 77 is a partial enlarged view of a display panel of the presentinvention.

FIG. 78 is a partial enlarged view of a display panel of the presentinvention.

FIGS. 79A to 79C show an example of a light emitting element.

FIGS. 80A to 80C show an example of a light emitting element.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiment modes of the present invention are explainedwith reference to the drawings. However, the present invention is notlimited to the following description. As is easily known to a personskilled in the art, the mode and the detail of the invention can bevariously changed without departing from the spirit and the scope of thepresent invention. Thus, the present invention is not interpreted whilelimiting to the following description of the embodiment modes.

A semiconductor device of the present invention, in which a circuit isformed over a substrate, includes a connection terminal portion to beconnected to an FPC (Flexible Printed Circuit). The connection terminalportion includes a plurality of connection terminals, at least one ofwhich is connected to a plurality of FPC terminals. Hereinafter, thisconnection terminal is referred to as a composite connection terminal.In addition, a connection terminal connected to one FPC terminal as apair is hereinafter referred to as a reference connection terminal.

By connecting a plurality of FPC terminals and a composite connectionterminal as described above, contact resistance can be decreased.

Note that in a connection terminal, a surface electrode to be connectedto an

FPC terminal is referred to as a connection pad. In other words, asurface electrode which is part of a connection terminal is referred toas the connection pad. In addition, a surface electrode of an FPCterminal to be connected to a connection terminal is referred to as anFPC pad. In other words, a surface electrode which is part of the FPCterminal is referred to as the FPC pad. Furthermore, the width betweenadjacent connection pads is referred to as a connection pitch, and thewidth between adjacent FPC pads is referred to as an FPC pitch.

Although connection pads in one connection terminal portion of thesemiconductor device of the present invention are arranged to have equalconnection pitches, it is not limited to the equal connection pitches.

Therefore, an FPC terminal array does not need to be changed, and an FPCcan be used without any change in the specification. Thus, the FPC canbe made versatile.

Note that in the above explanation, the FPC is connected, as an example,in the connection terminal portion of the semiconductor device; however,the present invention is not limited thereto. For example, an IC(semiconductor integrated circuit) chip, a printed wiring board (PWB), aprogrammable logic device (such as a field programmable gate array(FPGA) or a complex programmable logic device (CPLD)), or the like maybe connected.

Embodiment Mode 1

In this embodiment mode, the case of applying the present invention to adisplay panel is explained. In addition, in this embodiment mode, astructure in which a composite connection terminal includes a compositeconnection pad is explained. In other words, explanation is made on astructure in which a composite connection terminal includes oneconnection pad (composite connection pad) and the composite connectionpad is electrically connected to a plurality of FPC pads through ananisotropic conductive film.

First, a module in which a display panel is connected to an FPC in thisembodiment mode is shown in FIG. 1A. Note that such a module and a mainbody of a display panel are collectively referred to as a display devicein this specification.

A pixel portion 106 and peripheral driver circuits (a scan line drivercircuit 105 and a signal line driver circuit 104) for driving the pixelportion 106 are formed over a substrate 101. Then, the substrate 101 isattached to an opposite substrate 102. In the pixel portion 106, aplurality of signal lines which extend in a column direction from thesignal line driver circuit 104 is arranged in a row direction side byside. In addition, in the pixel portion 106, a plurality of scan linesthat extend in a row direction from the scan line driver circuit 105 isarranged in a column direction side by side. In the pixel portion 106, aplurality of pixels including display elements are arranged.

Note that the display element can be of various types. For example, adisplay medium in which contrast varies by an electro-magnetic actioncan be employed, such as an EL element (an organic EL element, aninorganic EL element, or an EL element containing an organic materialand an inorganic material), an electron emitting element, a liquidcrystal element, electronic ink, an optical diffractive element, adischarge element, a digital micro-mirror device (DMD), a piezoelectricelement, or a carbon nanotube. Note that examples of display devicesusing the above display elements are as follows: an EL display, as anEL-panel display device using an EL element; a field emission display(FED) or an SED flat-panel display (SED: surface-conductionelectron-emitter display), as a display device using an electronemitting element; a liquid crystal display, as a liquid-crystal paneldisplay device using a liquid crystal element; electronic paper, as adigital-paper display device using electronic ink; a grating light valve(GLV) display, as a display device using an optical diffractive element;a plasma display, as a PDP (Plasma Display Panel) display using adischarge element; a digital light processing (DLP) display device, as aDMD-panel display device using a digital micro-mirror device; apiezoelectric ceramic display, as a display device using a piezoelectricelement; a nano emissive display (NED), as a display device using acarbon nanotube; and the like.

The substrate 101 is connected to an FPC 103 in a connection terminalportion. A signal and power which are necessary for the scan line drivercircuit 105, the signal line driver circuit 104, and the pixel portion106 are supplied through the FPC 103 to the display panel.

Subsequently, a schematic perspective view of a partial cross sectionshowing a connection state between the substrate 101 and the FPC 103 inthe vicinity of a dotted line 107 is shown in FIG. 1B. Note that adirection corresponding to a line a-b in FIG. 1A is indicated by a linea-b in FIG. 1B to make a cross-sectional direction easy to understand.

A plurality of connection pads are formed over the substrate 101. Theplurality of connection pads include a reference connection pad 112 anda composite connection pad 113. The plurality of connection pads arearranged with partitions 114 having approximately equal widthsinterposed therebetween. Note that the order of the arrangement of thereference connection pad 112 and the composite connection pad 113 hereis not limited to that shown in FIG. 1B.

The FPC 103 is provided with equally-spaced FPC pads 111 havingapproximately equal widths. Then, a surface of the substrate 101 overwhich the connection pads (the reference connection pad 112 and thecomposite connection pad 113) are formed is attached to a surface of theFPC 103 over which the FPC pads 111 are formed, so as to oppose eachother.

Note that one corresponding FPC pad 111 is provided over the referenceconnection pad 112 as a pair so as to face the reference connection pad112. In addition, a plurality of corresponding FPC pads 111 are providedover the composite connection pad 113 so as to face the compositeconnection pad 113. Furthermore, the connection pads (the referenceconnection pad 112 and the composite connection pad 113) and the FPCpads 111 are electrically connected to each other with an anisotropicconductive film. Note that the anisotropic conductive film is not shownhere to make the structure easy to understand.

Subsequently, a schematic diagram of the structure of the display panelshown in FIGS. 1A and 1B is shown in FIG. 2. The scan line drivercircuit 105, the signal line driver circuit 104, and the pixel portion106 are formed over the substrate 101. In addition, a connectionterminal portion 201 is formed over the substrate 101. The connectionterminal portion 201 is provided with the reference connection pad 112which is part of a reference connection terminal and the compositeconnection pad 113 which is part of a composite connection terminal.Note that in FIG. 2, the number and the array of the referenceconnection pads 112 and the composite connection pads 113 are notlimited to those shown in the diagram.

A plurality of scan lines 206 are arranged in a row direction extendingfrom the scan line driver circuit 105 to the pixel portion 106. Inaddition, a plurality of signal lines 207 are arranged in a columndirection extending from the signal line driver circuit 104 to the pixelportion 106. In the pixel portion 106, a plurality of pixels 205 arearranged in matrix so as to correspond to the scan lines 206 and thesignal lines 207. Note that the phrase “pixels are arranged in matrix”includes the case of delta array in which three color elements (forexample, RGB) that are the smallest unit of an image are arranged in aso-called delta configuration in the case of performing full colordisplay using three color elements, as well as the case of stripe arrayin which pixels are arranged in a grid of a combination of verticalstripes and lateral stripes.

Note that each of the pixels 205 is provided with a pixel electrode. Anopposite electrode 202 is formed to cover the pixel portion 106. Then, adisplay element is formed by sandwiching a display medium between thepixel electrode and the opposite electrode 202. Further, the pixelportion 106 includes a power supply line 208, through which power issupplied to the pixel electrode of each pixel 205.

Since the connection terminal portion 201 is provided with the compositeconnection pad 113 which is part of the composite connection terminal,the display panel of this embodiment mode can reduce power consumption.Therefore, in particular, a connection terminal to which a power supplypotential serving as a power source is inputted is preferably formed tobe the composite connection terminal.

In addition, when a connection terminal to which a video signal forcontrolling lighting and non-lighting of the pixel 205 is inputted isalso formed to be the composite connection terminal, defective displaycan be prevented.

In the display panel of this embodiment mode, the connection terminalportion 201 may be formed inside the edge of the substrate 201 as shownin FIG. 2, or may be formed to be in contact with the edge of thesubstrate as shown in FIG. 3. In addition, the composite connection pads113 may be provided on both ends of the connection terminal portion 201as shown in FIG. 7. Furthermore, a plurality of connection terminalportions may be provided. For example, a connection terminal portion4001 and a connection terminal portion 4002 may be provided as shown inFIG. 40. Note that different FPCs are separately connected to theconnection terminal portion 4001 and the connection terminal portion4002. Either or both of the connection terminal portions may include acomposite connection pad.

FIGS. 1A and 1B show the structure in which the scan line driver circuit105, the signal line driver circuit 104, and the pixel portion 106 areintegrated over the substrate; however, the scan line driver circuit 105and the signal line driver circuit 104 may be formed on an IC chip,which may be mounted by COG (Chip On Glass) or the like as shown in FIG.8. Note that the IC chip means an integrated circuit formed over asubstrate and separated into a chip. In particular, for the IC chip, acircuit which is formed by element separation or the like using asingle-crystal silicon wafer as a substrate and separated into anarbitrary shape by cutting the single-crystal silicon wafer is suitable.

Furthermore, a connection structure between the connection pads (thereference connection pad 112 and the composite connection pad 113) andthe FPC pads 111 is explained in detail with reference to FIGS. 4B and4C. Electrical connection between the reference connection pad 112 andthe FPC pad 111 is made by pressure bonding with the use of ananisotropic conductive film 411. Note that the anisotropic conductivefilm 411 may contain a conductive particle 421 as shown in FIG. 4C. Theconductive particle 421 is a particle having a lower resistance thanthat of the anisotropic conductive film 411. Therefore, the contactresistance between the reference connection pad 112 and the FPC pad 111can be decreased. Note that FIGS. 4B and 4C show a connection portionbetween the reference connection pad 112 and the FPC pad 111, and thesame applies to the connection between the composite connection pad 113and the FPC pad 111.

Moreover, characteristics of the connection terminal portion on thesubstrate 101 side is explained with reference to FIG. 4A. FIG. 4A is across-sectional view of the connection terminal portion of the substrate101. Composite connection pads 113 a and 113 b each having differentwidths correspond to the composite connection pads 113 shown in FIG. 1B.

Then, assuming that the reference connection pad 112 has a line width401, the composite connection pad 113 a has a line width 402, thecomposite connection pad 113 b has a line width 403, and the partition114 provided between each connection pad (the reference connection pad112 and the composite connection pads 113 a and 113 b) and an adjacentconnection pad has a width (also referred to as a connection pitch) 404,the length of the line width 402 corresponds to a total length of twoline widths 401 and the width 404. In addition, the line width 403approximately corresponds to a total length of three line widths 401 andtwo widths 404. In other words, the length of the line width of thecomposite connection pad 113 in FIG. 1B corresponds to a total length ofn (n is an integer more than 1) line widths of the reference connectionpad 112 and (n−1) widths (also referred to as a connection pitch) of thepartition.

Therefore, FIG. 1B shows the case where the composite connection pad 113is electrically connected to two FPC pads 111; however, it goes withoutsaying that the invention is not limited thereto. In other words, thecomposite connection pad 113 may be electrically connected to three FPCpads 111, four FPC pads 111, or more than four FPC pads 111.

The case where the composite connection pad 113 is electricallyconnected to two FPC pads 111 is as shown in FIG. 5A. The compositeconnection pad 113 a is connected to two FPC pads 111 through theanisotropic conductive film 411. In addition, the case where thecomposite connection pad 113 b is electrically connected to three FPCpads 111 is as shown in FIG. 5B. The composite connection pad 113 b isconnected to three FPC pads 111 through the anisotropic conductive film411. Note that the anisotropic conductive film 411 may contain theconductive particle 421 as shown in FIG. 4C.

Note that in the connection terminal portion of the display paneldescribed in this embodiment mode, the contact resistance of thecomposite connection terminal can be made lower than the contactresistance of the reference connection terminal. Therefore, in the caseof supplying a power supply potential serving as a power source or thelike that consumes a large amount of power, it is preferably supplied tothe display panel through a composite connection terminal connected to aplurality of FPC terminals. In other words, a connection terminal towhich a power supply potential serving as a power source may be formedto be the composite connection terminal. In accordance with that, theresistance of a power supply line can be decreased, a voltage drop inthe power supply line can be suppressed, and defective display can beprevented.

When the composite connection terminal includes the composite connectionpad, the contact resistance of the composite connection terminal is notincreased even if misalignment of the connection terminal with the FPCterminal in a line width direction is caused in attachment of thedisplay panel and the FPC. Hereinafter, explanation is made withreference to FIGS. 6A and 6B.

FIG. 6A is a cross-sectional view showing the reference connection padand the FPC pad connected to each other through the anisotropicconductive film in the case where misalignment of the connectionterminal with the FPC terminal in a line width direction is not causedin attachment of the display panel and the FPC. In other words, thecenter of the line width of the reference connection pad 112 is almostaligned with that of the FPC pad 111. Then, FIG. 6D corresponds to a topview of FIG. 6A. Note that a region of the FPC pad 111 which does notoverlap the reference connection pad 112 has a width s.

FIG. 6B is a cross-sectional view showing the reference connection padand the FPC pad connected to each other through the anisotropicconductive film in the case where misalignment of the connectionterminal with the FPC terminal in a line width direction is caused inattachment of the display panel and the FPC. Then, FIG. 6E correspondsto a top view of FIG. 6B. As shown in FIGS. 6B and 6E, the FPC pad 111corresponding to the reference connection pad 112 as a pair ismisaligned in a line width direction; therefore, a non-overlap region isgenerated in the connection pad 112, and the non-overlap region has awidth g. Note that a non-overlap region which is enlarged in the FPC pad111 has a width t. The width g and the width t are approximately equalto each other. Therefore, a connection area is reduced by the width g.

On the other hand, FIG. 6C is a cross-sectional view showing thecomposite connection pad and the FPC pads connected to each otherthrough the anisotropic conductive film in the case where misalignmentof the connection terminal with the FPC terminal in a line widthdirection is caused in attachment of the display panel and the FPC.Then, FIG. 6F corresponds to a top view of FIG. 6C. In the connectionbetween the composite connection pad 113 and the FPC pads 111 shown inFIGS. 6C and 6F, a non-overlap region is only generated in one of theplurality of FPC pads 111 connected to the composite connection pad 113even if misalignment is caused. Then, the non-overlap region has a widtht. Furthermore, in the case where the FPC pad 111 is wider than thereference connection pad 112, the region s of the FPC pad 111, whichoverlaps the partition 114 when misalignment is not caused, overlaps thecomposite connection pad 113. Therefore, a connection area is enlarged.The enlarged area has a width s. As the number of FPC pads 111 connectedto one composite connection pad 113 is increased, the influence ofreduction in connection area due to the generation of the non-overlapregion is lessened. In the composite connection pad 113, a connectionarea may be enlarged. Therefore, the contact resistance of the compositeconnection terminal with the FPC terminal can be decreased even ifmisalignment of the connection terminal with the FPC terminal in a linewidth direction is caused in attachment of the display panel and theFPC.

Accordingly, the contact resistance of the composite connection terminaland the plurality of FPC terminals described in this embodiment mode canbe made 5Ω or less, preferably 1Ω or less.

Embodiment Mode 2

In this embodiment mode, structures of the connection pads (thereference connection pad 112 and the composite connection pad 113) whichare part of the connection terminals (the reference connection terminaland the composite connection terminal) described in Embodiment Mode 1and a wire extending from the connection pads into a sealing region areexplained in detail.

Note that the display panel to be described in this embodiment mode isparticularly suitable for a display panel having a structure in whichperipheral driver circuits (a scan line driver circuit and a signal linedriver circuit) for driving a pixel are integrated with a pixel portion.In other words, the peripheral driver circuit includes a thin filmtransistor (also referred to as a TFT) and the like formed at the sametime as the formation of a thin film transistor included in the pixel. Aschematic diagram of a display panel having such a structure is shown inFIG. 9. Note that the connection terminal portion 201 is not necessarilyformed inside the edge of the substrate 101 as in this structure, andmay be formed in contact with the edge of the substrate 101 as shown inFIG. 3.

In the display panel of this structure, a pixel portion 106 and aperipheral driver circuit formed over the substrate 101 are sandwichedbetween the substrate 101 and an opposite substrate and are sealed in asealing region 901. Note that the sealing may be performed by any ofsolid sealing, vacuum sealing, gas sealing, liquid sealing, and thelike. For example, a resin or the like can be used for solid sealing. Inaddition, He (helium), Ar (argon), N (nitrogen), or the like can be usedfor gas sealing. Further, liquid paraffin, a silicon liquid, or the likecan be used for liquid sealing.

Here, an enlarged view of a region surrounded by a dotted line 902 isshown in FIG. 10. The connection terminal portion includes the referenceconnection pad 112 and composite connection pads (the compositeconnection pad 113 a and the composite connection pad 113 b). Thereference connection pad 112 and a wire 1001 are formed with acontinuous conductive film. The line width of the wire 1001 is smallerthan the line width of the reference connection pad 112. Specifically,the line width of the wire 1001 is half or less the line width of thereference connection pad 112, more preferably, one-third or less. Inaddition, the composite connection pad 113 a and a wire 1002, and thecomposite connection pad 113 b and a wire 1003 are also formed withrespective continuous conductive films. Then, the wire 1002 and the wire1003 have line widths approximately equal to those of the compositeconnection pad 113 a and the composite connection pad 113 b,respectively.

Note that the composite connection pad 113 a has a total width of twoline widths of the reference connection pad 112 and the width of oneconnection pitch; however, the invention is not limited thereto. Inaddition, the composite connection pad 113 b has a total width of threeline widths of the reference connection pad 112 and two widths of theconnection pitch; however, the invention is not limited thereto. Inaddition, as shown in FIG. 10, the connection terminal portion mayinclude composite connection pads having different widths, or mayinclude a plurality of composite connection pads having the same width.In addition, the connection terminal portion may include one compositeconnection pad or more. The line widths of the wire 1001, the wire 1002,and the wire 1003 in a wiring portion are those in the vicinity of thesealing region 901, and they may have different line widths furtherinside the pixel portion. In addition, the number and the array order ofthe reference connection pad 112, the composite connection pad 113 a,and the composite connection pad 113 b are not limited to thosedescribed above.

In other words, in the structure shown in FIG. 10, the wire formed witha conductive film continuous with the reference connection pad is narrowin width in the sealing region. On the other hand, the wire formed witha conductive film continuous with the composite connection pad may havethe same line width as the composite connection pad also in the sealingregion.

Therefore, since the area of the wire formed with a conductive filmcontinuous with the reference connection pad 112 becomes smaller in thesealing region, the adhesion between the substrate 101 and the oppositesubstrate attached thereto can be improved. In addition, the wiresformed with layers continuous with the composite connection pads (thecomposite connection pad 113 a and the composite connection pad 113 b)have the same widths as those of the composite connection pads;therefore, the resistance of the wires can be decreased. Note that thenumber of the composite connection pads is preferably smaller than thatof the reference connection pads 112 in order to further improve theadhesion.

In addition, an enlarged view of another structure of the regionsurrounded by the dotted line 902 is shown in FIG. 11. This structurecan further improve the adhesion between the substrate 101 and theopposite substrate attached thereto.

In the structure of FIG. 11, the wire 1001 formed with a conductive filmcontinuous with the reference connection pad 112 is the same as thatshown in FIG. 10. Then, the composite connection pad 113 a includes anarrow wire portion 1101 and a wide wire portion 1102 in the wiringportion. In addition, the composite connection pad 113 b also includes anarrow wire portion 1103 and a wide wire portion 1104 in the wiringportion.

In other words, in each of the composite connection pads (the compositeconnection pad 113 a and the composite connection pad 113 b), a wire isformed with the same conductive film across the sealing region 901. Thewire is narrow in the sealing region 901 and is wide within a regionwhere the substrate and the opposite substrate are attached to eachother. Preferably, the line width of the narrow wire is one third orless of the line width of the reference connection pad 112, and the linewidth of the wide wire is approximately equal to the line width of thecomposite connection pad. In addition, the length of the narrow wire isin the range of three times to ten times the width of the sealing region901. Consequently, the adhesion between the substrate and the oppositesubstrate is improved. In addition, since the length of the narrow wireis short, an increase in resistance can be suppressed.

An enlarged view of another structure of the region surrounded by thedotted line 902 is shown in FIG. 12. This structure can improve theadhesion between the substrate 101 and the opposite substrate attachedthereto while suppressing an increase in wire resistance.

In the structure shown in FIG. 12, the wire 1001 formed with aconductive film continuous with the reference connection pad 112 is thesame as that shown in FIG. 10. Then, the composite connection pad 113 aincludes a narrow wire portion 1201 and a wide wire portion 1202 in thewiring portion. In addition, the composite connection pad 113 b alsoincludes a narrow wire portion 1203 and a wide wire portion 1204 in thewiring portion.

In other words, in each of the composite connection pads (the compositeconnection pad 113 a and the composite connection pad 113 b), a wire isformed with the same conductive film across the sealing region 901. Thewire is divided into a plurality of narrow wires in the sealing region901, and the plurality of narrow wires converge and become a wide wireinside a region where the substrate and the opposite substrate areattached to each other. Preferably, the line width of each narrow wireis one third or less of the line width of the composite connection pad,and the line width of the wide wire is approximately equal to the linewidth of the composite connection pad. In addition, the length of thenarrow wire is in the range of three times to ten times the width of thesealing region 901. Consequently, the adhesion between the substrate andthe opposite substrate is improved. In addition, since the length of thenarrow wire is short, an increase in resistance can be suppressed.

Although the composite connection pad 113 a having a total width of twoline widths of the reference connection pad 112 and a width of oneconnection pitch is divided into two narrow wire portions 1201 in thesealing region 901 in the structure shown in FIG. 12, the invention isnot limited thereto. Furthermore, the composite connection pad 113 bhaving a total width of three line widths of the reference connectionpad 112 and two widths of the connection pitch is divided into threenarrow wire portions 1203 in the sealing region 901; however, theinvention is not limited thereto. In addition, as shown in FIG. 44, in awire portion having the same width as that of the composite connectionpad 113 a, part of the wire which intersects with the sealing region 901may be removed to form a plurality of narrow wire portions 4401, and thewire may have a wide wire portion 4402 in a pixel portion. In the samemanner, in the wire portion having the same width as that of thecomposite connection pad 113 b, part of the wire which intersects withthe sealing region 901 may be removed to form a plurality of narrow wireportions 4403, and the wire may have a wide wire portion 4404 in a pixelportion.

Note that power supply potentials may be different in the case where thedisplay device performs full color display using RGB color elements. Inthat case, as shown in FIG. 41, a power supply potential of a colorelement R is supplied to a pixel through a wire 4101R connected to thecomposite connection pad 113, a wire 4201R connected to the wire 4101R,and a power supply line 208R connected to the wire 4201R. In addition, apower supply potential of a color element G is supplied to a pixelthrough a wire 4101G, a wire 4201G connected to the wire 4101G, and apower supply line 208G connected to the wire 4201G. A power supplypotential of a color element B is supplied to a pixel through a wire4101B, a wire 4201B connected to the wire 4101B, and a power supply line208B connected to the wire 4201B.

In order to improve the adhesion with the FPC in the connection terminalportion, a depression 4701 may be provided in the connection pads (thereference connection pad 112, the composite connection pad 113 a, andthe composite connection pad 113 b) as shown in FIG. 47. Note that aplurality of depressions 4701 are preferably provided for one connectionpad. However, the number and the shape of the depressions 4701 are notlimited to those shown in FIG. 47. Therefore, the depression may havenot only such a circular shape as shown in FIG. 47 but also a squareshape or a triangular shape. Alternatively, a depression 5001 formed ina stripe shape in a direction perpendicular to a line width direction ofthe connection pad may be provided as shown in FIG. 50, or a depression5101 formed in a stripe shape in a line width direction of theconnection pad may be provided as shown in FIG. 51.

In addition, the structure of the composite connection pad is also notlimited to those described above. For example, the composite connectionpad may have a structure where a plurality of electrodes having the sameshape as the reference connection pad are joined at an electrode jointportion 3601 as shown in FIG. 36. In other words, two electrodes eachhaving the same line width as the reference connection pad 112 arejoined by the electrode joint portion 3601, thereby forming thecomposition connection pad 113 a. In addition, three electrodes eachhaving the same line width as the reference connection pad 112 arejoined by the electrode joint portion 3601, thereby forming thecomposition connection pad 113 b. Note that the composite connection padmay be formed to be continuous using one conductive film, or theelectrodes and the electrode joint portion 3601 may be formed withdifferent conductive films.

In addition, electrodes serving as the connection pads (the referenceconnection pad 112, the composite connection pad 113 a, and thecomposite connection pad 113 b) forming the connection terminal may beformed with a different conductive film from that used for a wireextending from each connection terminal. For example, an electrode 4801in the connection terminal portion is formed with a conductive filmcontinuous with a wire 4802 extending into the sealing region as shownin FIG. 48. Then, an electrode serving as a pad is formed over theelectrode 4801. In other words, the reference connection pad 112 isformed over the electrode 4801 forming the reference connectionterminal, and each of the composite connection pad 113 a and thecomposite connection pad 113 b is formed over a plurality of electrodes4801 serving as the composite connection terminal.

In such a structure, the connection pads (the reference connection pad112, the composite connection pad 113 a, and the composite connectionpad 113 b) are formed with a material of a transparent conductive filmof a bottom emission display device, and the electrode 4801 and the wire4802 are formed with a metal material. As an example of the transparentconductive film, ITO, TZO, CTO, or the like can be given.

Note that the connection pad is not limited to an electrode formed withone conductive film. In other words, other conductive films 4903 havinga smaller area than an electrode 4901 may be formed over the electrode4901, an electrode 4902 a, and an electrode 4902 b as shown in FIG. 49.In other words, the reference connection pad is formed with theelectrode 4901 and the conductive film 4903. The composite connectionpad is formed with the electrode 4902 a and the conductive film 4903.The composite connection pad is formed with the electrode 4902 b and theconductive film 4903. As described above, the connection pad alsoincludes an exposed conductive region when the connection terminalportion is seen from above.

In such a structure, the electrode 4901, the electrode 4902 a, and theelectrode 4902 b are formed with a material of a transparent conductivefilm of a top emission display device, and the conductive film 4903 isformed with a material of an auxiliary wire. As an example of thetransparent conductive film, ITO, TZO, CTO, or the like can be given.

Note that the structures of a connection pad and a wire connected to theconnection pad, which can be applied to the invention, are not limitedto those described above. In addition, the above-described structurescan be used in combination.

Embodiment Mode 3

In this embodiment mode, a structure of a display device is explained.In particular, explanation is made in this embodiment mode, focusing onthe connection structure between a composite connection pad and anopposite electrode.

First, a first structure of this embodiment mode is explained withreference to FIG. 13. Note that components in common with FIG. 2 aredenoted by common reference numerals, and explanation thereof isomitted. In the first structure, a wide wire 1301 which is part of theopposite electrode 202 is formed across the signal line driver circuit104, and is connected to a wire extending from the composite connectionpad 113 through a contact hole 1302. In this case, the wide wire 1301 ispreferably formed to be wider than the line width of the compositeconnection pad 113. Then, contact resistance can be decreased since thecontact hole 1302 can be enlarged. In other words, as shown in FIG. 45,the wire 1204 extending from the composite connection pad 113 b isconnected to a wide wire 1301 which is part of the opposite electrode202 through a contact hole 4501 within the pixel portion across thesealing region 901. In this case, the wire 1204 can be formed to havethe same width as the line width of the composite connection pad 113 a;therefore, the width of the contact hole 4501 can also be enlarged. Inother words, the width of the contact hole 4501 can be made larger thanthe line width of the reference connection pad 112. Note that componentsin common with FIG. 12 are denoted by common reference numerals, andexplanation thereof is omitted. Alternatively, the wire 1204 and theopposite electrode 202 may be connected to each other through not onlyone contact hole but a plurality of contact holes 4601 as shown in FIG.46.

Subsequently, a second structure of this embodiment mode is explainedwith reference to FIG. 14. Note that components in common with FIG. 2are denoted by common reference numerals, and explanation thereof isomitted. In the second structure, a wire 1401 extending from thecomposite connection pad 113 has approximately equal width to thecomposite connection pad 113 and further includes a wide wire 1402. Thewidth of this wire 1402 is approximately equal to that of the signalline driver circuit 104. Then, a wire 1403 connected to the wire 1402passes through the signal line driver circuit 104 and connected to theopposite electrode 202 through a contact hole 1404 by a multilayerwiring structure. Note that the contact hole 1404 is formed in a regionbetween the pixel portion 106 and the signal line driver circuit 104.Thus, since the composite connection pad 113, and the wire 1401 and thewire 1402 having low wire resistance are formed with a continuousconductive film without a contact hole, resistance of line from thecomposite connection pad 113 to the opposite electrode 202 can bedecreased.

Subsequently, a third structure of this embodiment mode is explainedwith reference to FIG. 15. Note that components in common with FIG. 2are denoted by common reference numerals, and explanation thereof isomitted. In the third structure, the signal line driver circuit 104 isformed on the side opposite to the connection terminal portion 201 withthe pixel portion 106 therebetween. In such a structure, the oppositeelectrode 202 is connected to a wire extending from the compositeconnection pad 113 through a contact hole 1501 without extending acrossthe signal line driver circuit 104. In addition, since the length ofline from the composite connection pad 113 to the opposite electrode 202is short, the resistance of this line can be decreased.

Subsequently, a fourth structure of this embodiment mode is explainedwith reference to FIG. 16. Note that components in common with FIG. 2are denoted by common reference numerals, and explanation thereof isomitted. In the fourth structure, a wire 1603 connected to the compositeconnection pad 113 is connected to a wire 1601 arranged so as tosurround the signal line driver circuit 104. The wire 1601 is wide atleast in a region between the signal line driver circuit 104 and thepixel portion 106, where it is connected to the opposite electrode 202through a contact hole 1602. Note that a further decrease in resistancecan be achieved when the composite connection pad 113, the wire 1603,and the wire 1601 are formed with the same conductive film because acontact hole is not interposed.

Subsequently, a fifth structure of this embodiment mode is explainedwith reference to FIG. 17. Note that components in common with FIG. 2are denoted by common reference numerals, and explanation thereof isomitted. In the fifth structure, a wire 1703 connected to the compositeconnection pad 113 is connected to a wire 1701 arranged so as tosurround the signal line driver circuit 104 and the pixel portion 106.The wire 1701 is wide at least in a region between the signal linedriver circuit 104 and the pixel portion 106 and a region on the sideopposite thereto with the pixel portion 106 therebetween, where it isconnected to the opposite electrode 202 through a contact hole 1702.Note that a further decrease in resistance can be achieved when thecomposite connection pad 113, the wire 1703, and the wire 1701 areformed with the same conductive film because a contact hole is notinterposed. According to this structure, the wire 1701 is led around thepixel portion 106. Therefore, by using a conductive film formed from alow-resistance material for the wire 1701, an in-plane potential of theopposite electrode 202 can be equalized. Note that the oppositeelectrode 202 and the wire 1701 may be connected to each other inanother region. For example, as shown in FIG. 18, the wire 1701 is wideat least in a region between the scan line driver circuit 105 and thepixel portion 106 and a region on the side opposite thereto with thepixel portion 106 therebetween, where it may be connected to theopposite electrode 202 through the contact hole 1702.

Subsequently, a sixth structure of this embodiment mode is explainedwith reference to FIG. 19. Note that components in common with FIG. 2are denoted by common reference numerals, and explanation thereof isomitted. In the sixth structure, the composite connection pads 113 arearranged on both ends of the connection terminal portion 201. Inaddition, a wide wire 1901 a is formed between the scan line drivercircuit 105 and the pixel portion 106. In addition, a wide wire 1901 bis formed on the side opposite to the wire 1901 a with the pixel portion106 therebetween.

Then, a wire 1903 connected to one of the composite connection pads 113formed on both ends is connected to the wire 1901 a. In addition, a wire1903 connected to the other of the composite connection pads 113 formedon both ends is connected to the wire 1901 b.

Then, the wire 1901 a and the wire 1901 b are connected to the oppositeelectrode 202 through a contact hole 1902. Note that the wire 1901 a andthe wire 1901 b are preferably formed with a low-resistance conductivefilm. Then, an influence of voltage drop can be reduced, and an in-planepotential of the opposite electrode 202 can be equalized. In addition,either the wire 1901 a or the wire 1901 b may be provided; however, byarranging the wires on both sides of the pixel portion 106 as shown inFIG. 19, the influence of voltage drop can further be reduced. Inaddition, the invention is not limited to the case of providing wires onboth sides like the wire 1901 a and the wire 1901 b, the wire may bearranged so as to surround the pixel portion 106. In this case, in awire 2001 surrounding the pixel portion 106, at least one contact hole1902 is provided in each of a region between the pixel portion 106 andthe signal line driver circuit 104, a region on the side opposite to thesignal line driver circuit 104 with the pixel portion 106 therebetween,a region between the scan line driver circuit 105 and the pixel portion106, and a region on the side opposite to the scan line driver circuit105 with the pixel portion 106 therebetween as shown in FIG. 20. Then,the wire 2001 and the opposite electrode 202 are connected to each otherthrough the contact hole 1902.

Note that the structure of a display device to which the invention canbe applied is not limited to those described above.

Embodiment Mode 4

In this embodiment mode, a structure of a display device is explained.In particular, explanation is made in this embodiment mode, focusing ona structure of connection between a composite connection pad and a pixelelectrode.

First, a first structure of this embodiment mode is explained withreference to FIG. 21. Note that components in common with FIG. 2 aredenoted by common reference numerals, and explanation thereof isomitted. In the first structure, a wire 2102 is formed to surround thesignal line driver circuit 104. Then, a wire 2101 connected to thecomposite connection pad 113 is further connected to the wire 2102. Asfor the wire 2102, a power supply line 208 extending to the pixelportion 106 is formed. With such a structure, an influence of voltagedrop can be reduced, and a potential of each power supply line 208 canbe equalized. Furthermore, by using a low-resistance conductive film forthe wire 2102, the influence of voltage drop can further be reduced. Inaddition, in order to suppress variations in power supply potentialsupplied to each pixel in each row of the pixel portion 106, the wire2102 may be led around the pixel portion 106. That case is as shown by awire 2201 in FIG. 22. In this case, the wire 2201 and the power supplyline 208 are connected to each other in a region between the pixelportion 106 and the signal line driver circuit 104, and the wire 2201and the power supply line 208 are also connected on the side opposite tothe signal line driver circuit 104 with the pixel portion 106therebetween. Note that the wire 2201 is made wider than the line widthof the power supply line 208. Alternatively, a material used for thewire 2201 is made to have lower resistance than that of a material usedfor the power supply line 208. Alternatively, these are combined.Accordingly, the influence of voltage drop can further be reduced.

Subsequently, a second structure of this embodiment mode is explainedwith reference to FIG. 23. Note that components in common with FIG. 2are denoted by common reference numerals, and explanation thereof isomitted. In the second structure, the signal line driver circuit 104 isformed on the side opposite to the connection terminal portion 201 withthe pixel portion 106 therebetween. In addition, from the compositeconnection pad 113 to a wide wire 2301 and a wide wire 2302 are formedwith one continuous conductive film. Furthermore, the line width of thewide wire 2301 is approximately equal to that of the compositeconnection pad 113, and the line width of the wide wire 2302 isapproximately equal to the width of the pixel portion 106 in a rowdirection. Then, the power supply line 208 connected to the wide wire2302 is formed to extend to the pixel portion 106. According to thisstructure, from the connection pad 113 to the power supply line 208 canbe formed with one continuous wire without a contact hole; therefore,resistance can be decreased. Consequently, the influence of voltage dropcan further be reduced.

Embodiment Mode 5

In this embodiment mode, a structure of a display device is explained.In particular, explanation is made in this embodiment mode, focusing ona structure of connection between a composite connection pad, and thepixel electrode and the opposite electrode.

First, a first structure of this embodiment mode is explained withreference to FIG. 24. Note that components in common with FIG. 2 aredenoted by common reference numerals, and explanation thereof isomitted. In the first structure, the signal line driver circuit 104 isformed on the side opposite to the connection terminal portion 201 withthe pixel portion 106 therebetween. With such a structure, the oppositeelectrode 202 is connected to a wire extending from the compositeconnection pad 113 through a contact hole 1501 without extending acrossthe signal line driver circuit 104. In addition, from the compositeconnection pad 113 to a wide wire 2301 and a wide wire 2302 are formedusing one continuous conductive film. Then, the line width of the widewire 2301 is approximately equal to that of the composite connection pad113, and the line width of the wide wire 2302 is approximately equal tothe width of the pixel portion 106 in a row direction. Then, the powersupply line 208 connected to the wide wire 2302 is formed to extend tothe pixel portion 106. According to this structure, from the compositeconnection pad 113 to the power supply line 208 can be formed with onecontinuous wire without a contact hole; therefore, resistance can bedecreased.

Subsequently, a second structure of this embodiment mode is explainedwith reference to FIG. 25. Note that components in common with FIG. 2are denoted by common reference numerals, and explanation thereof isomitted. The second structure includes at least two composite connectionpads 113. Then, from one of the composite connection pads 113 to a widewire 1401 and a wide wire 1402 are formed with one continuous conductivefilm. Then, the line width of the wide wire 1401 is approximately equalto that of the composite connection pad 113, and the line width of thewide wire 1402 is approximately equal to the width of the pixel portion106 in a row direction. In addition, a wire 2101 connected to the othercomposite connection pad 113 is connected to a wire 2102 formed tosurround the signal line driver circuit 104. Then, the wide wire 1402 isconnected to the opposite electrode 202 through a contact hole 1404 by awire 1403 having a multilayer structure. This contact hole 1404 isformed between the signal line driver circuit 104 and the pixel portion106. In addition, the power supply line 208 is formed from the wire 2102to the pixel portion 106.

Subsequently, a third structure of this embodiment mode is explainedwith reference to FIG. 26. Note that components in common with FIG. 2are denoted by common reference numerals, and explanation thereof isomitted. The third structure includes at least two composite connectionpads 113. A wide wire 1301 which is part of the opposite electrode 202is formed across the signal line driver circuit 104, and is connected toa wire extending from one of the composite connection pads 113 through acontact hole 1302. In this case, the wide wire 1301 is preferably formedto be wider than the line width of the composite connection pad 113.Then, contact resistance can be decreased since the contact hole 1302can be enlarged. In addition, a wire 2101 connected to the othercomposite connection pad 113 is connected to a wire 2102 formed tosurround the signal line driver circuit 104. In addition, the powersupply line 208 is formed from the wire 2102 to the pixel portion 106.

Embodiment Mode 6

In this embodiment mode, a cross-sectional structure of a connectionterminal is explained in more detail. Note that in this embodiment mode,a cross-sectional structure of a pixel portion and a connection terminalportion of a display device having an EL element in a pixel isdescribed; however, a display device to which the present invention canbe applied is not limited thereto.

In the display device to which the present invention can be applied, asemiconductor layer of a thin film transistor (also referred to as aTFT) incorporated in a display panel may be a crystalline semiconductorfilm or an amorphous semiconductor film. As the crystallinesemiconductor film, a polysilicon (p-Si) film, for example, can be used.As the amorphous semiconductor film, an amorphous silicon (a-Si:H) filmcan be used. Furthermore, a so-called microcrystalline silicon film maybe used. In addition, the thin film transistor can have a structure suchas a top gate structure in which a gate electrode is provided over asemiconductor layer or a bottom gate structure in which a gate electrodeis provided below a semiconductor layer.

First, in the case of employing a crystalline semiconductor film as thesemiconductor layer, cross sections of a connection terminal portion anda pixel portion of a display panel having a top-gate transistor areshown in FIGS. 52A and 52B.

A base film 5202 is formed over a substrate 5201. An insulatingsubstrate, a metal substrate, a semiconductor substrate, or the likesuch as a glass substrate, a quartz substrate, a plastic substrate, or aceramics substrate can be used as the substrate 5201.

The base film 5202 can be formed by a CVD method or a sputtering method.For example, a silicon oxide film, a silicon nitride film, a siliconoxynitride film, or the like which is formed by a CVD method using SiH₄,N₂O, NH₃, or the like as a source material can be employed.Alternatively, a laminate thereof may be used. Note that the base film5202 is provided to prevent an impurity from diffusing into thesemiconductor layer from the substrate 5201, and the base film 5202 isnot necessarily provided in the case of using a glass substrate or aquartz substrate as the substrate 5201.

An island-shaped semiconductor layer is formed over the base film 5202.In the semiconductor layer, a channel formation region 5203 where achannel is formed and an impurity region 5204 serving as a source regionor a drain region are formed. Then, a gate electrode 5206 is formed overthe channel formation region 5203 with a gate insulating film 5205therebetween.

The gate insulating film 5205 can be formed using a silicon oxide film,a silicon nitride film, a silicon oxynitride film, or the like by a CVDmethod or a sputtering method. In addition, the gate electrode 5206 canbe formed using an aluminum (Al) film, a copper (Cu) film, a thin filmcontaining aluminum or copper as its main component, a chromium (Cr)film, a tantalum (Ta) film, a tantalum nitride (TaN) film, a titanium(Ti) film, a tungsten (W) film, a molybdenum (Mo) film, or the like.

Note that a sidewall may be formed on the side of the gate electrode5206. The sidewall can be formed by forming a silicon compound such as asilicon oxide film, a silicon nitride film, or a silicon oxynitride filmto cover the gate electrode 5206, and then etching back it.

A first interlayer insulating film 5207 is formed over the gateelectrode 5206 and the gate insulating film 5205. The first interlayerinsulating film 5207 may include an inorganic insulating film as a lowerlayer and a resin film as an upper layer. As the inorganic insulatingfilm, a silicon nitride film, a silicon oxide film, a silicon oxynitridefilm, or a laminated film thereof can be used. As the resin film,polyimide, polyamide, acrylic, polyimide amide, epoxy, or the like canbe used.

In addition, a wire 5208 is formed over the first interlayer insulatingfilm 5207, and the wire 5208 is electrically connected to the impurityregion 5204 through a contact hole. As the wire 5208, a titanium (Ti)film, an aluminum (Al) film, a copper (Cu) film, an aluminum filmcontaining Ti, or the like can be used. Preferably, the wire 5208 has athree-layer structure, and has a structure including a titanium (Ti)film as a lower layer, an aluminum (Al) film thereover, and a titanium(Ti) film further thereover. With this structure, wire resistance, andcontact resistance with the impurity region 5204 can be decreased.

A second interlayer insulating film 5209 is formed over the wire 5208and the first interlayer insulating film 5207. As the second interlayerinsulating film 5209, an inorganic insulating film, a resin film, or alaminated layer thereof can be used. As the inorganic insulating film, asilicon nitride film, a silicon oxide film, or a silicon oxynitridefilm, or a laminated layer thereof can be used. As the resin film,polyimide, polyamide, acrylic, polyimide amide, epoxy, or the like canbe used. Note that the resin film is preferably used for planarization.

A pixel electrode 5210 is formed over the second interlayer insulatingfilm 5209. A material having a high work function is preferably used forthe pixel electrode 5210. Then, a transparent conductive film is usedfor the pixel electrode 5210 in the case of employing bottom emission inwhich light is extracted from the substrate 5201 side. Alternatively, alaminate of a transparent conductive film and such a thin metal film asto transmit light can be used. In addition, a light-reflecting metalfilm is preferably used for the pixel electrode 5210 in the case ofemploying top emission in which light is extracted from the sideopposite to the substrate 5201.

For example, as a material of the transparent conductive film, indiumtin oxide (ITO) in which tin oxide is added to indium oxide, indium zincoxide (IZO), cadmium tin oxide (CTO), zinc oxide (ZnO), tin oxide (TO),or the like can be used. By using ITO, a low-resistance pixel electrode5210 can be formed. In addition, by using IZO, a uniform film can beformed and minute processing can be performed.

For example, the light-reflecting metal film can be formed using asingle-layer film such as a titanium nitride (TiN) film, a chromium (Cr)film, a tungsten (W) film, a zinc (Zn) film, or a platinum (Pt) film; alaminated layer of a titanium nitride film and a film containingaluminum as its main component; a three-layer structure of a titaniumnitride film, a film containing aluminum as its main component, and atitanium nitride film; or the like. When the pixel electrode 5210 has alaminated structure, it can have low resistance as a wire and form afavorable ohmic contact. Further, the pixel electrode can function as ananode. By using the light-reflecting metal film, an anode which does nottransmit light can be formed.

An insulator 5211 is formed to cover end portions of the pixel electrode5210. For example, a positive type photosensitive acrylic resin film canbe used as the insulator 5211.

A layer 5212 containing an organic compound is formed over the pixelelectrode 5210. Further, an opposite electrode 5213 is formed over thelayer 5212 containing an organic compound.

For the opposite electrode 5213, a material having a low work functionis preferably used. For example, a metal thin film of aluminum (Al),silver (Ag), lithium (Li), calcium (Ca), an alloy thereof such as MgAg,MgIn, AlLi, CaF₂, or Ca₃N₂, or the like can be used.

In the case of employing bottom emission, the opposite electrode 5213 isformed using a metal thin film of aluminum (Al), silver (Ag), lithium(Li), calcium (Ca), an alloy thereof such as MgAg, MgIn, AlLi, CaF₂, orCa₃N₂, or the like to have such a thickness as to reflect light. Inaddition, in the case of employing top emission, the opposite electrodemay be formed using the above metal thin film to have such a thicknessas to transmit light, or using a combination of the above metal thinfilm having such a thickness as to transmit light and a transparentconductive film. Thus, the opposite electrode 5213 which can transmitlight can be formed.

A light emitting element 5215 is formed in a region where the layer 5212containing an organic compound is sandwiched between the oppositeelectrode 5213 and the pixel electrode 5210.

In addition, a transistor 5214 having the gate electrode 5206, theimpurity region 5204 serving as a source region or a drain region, andthe channel formation region 5203 is formed.

Subsequently, a structure of a connection terminal portion is explained.Note that a cross-sectional view of a connection terminal portion shownin FIG. 52A shows a cross section of a connection terminal in a linewidth direction.

Also in the connection terminal portion, the base film 5202 is formedover the substrate 5201, and the gate insulating film 5205 is formedthereover. However, the base film 5202 and the gate insulating film 5205are not necessarily formed in the connection terminal portion.

Furthermore, a first electrode 5221, a first electrode 5223, and a firstelectrode 5225 are formed over the gate insulating film 5205, and asecond electrode 5222, a second electrode 5224, and a second electrode5226 are formed over the first electrode 5221, the first electrode 5223,and the first electrode 5225, respectively.

Then, the first electrode 5221, the first electrode 5223, and the firstelectrode 5225, and the second electrode 5222, the second electrode5224, and the second electrode 5226 are electrically insulated bypartitions formed from the first interlayer insulating film 5207 and thesecond interlayer insulating film 5209.

Note that the first electrode 5221, the first electrode 5223, and thefirst electrode 5225 are formed from the same material as the gateelectrode 5206. In addition, the second electrode 5222, the secondelectrode 5224, and the second electrode 5226 are formed from the samematerial as the wire 5208. Preferably, each of the second electrode5222, the second electrode 5224, and the second electrode 5226 has athree-layer structure, which may include an aluminum film over atitanium film, and a titanium film thereover.

A reference connection terminal 5227 is formed with the first electrode5221 and the second electrode 5222. In addition, a composite connectionterminal 5228 is formed with the first electrode 5223 and the secondelectrode 5224. In addition, a reference connection terminal 5229 isformed with the first electrode 5225 and the second electrode 5226.Then, in the case of a structure as shown in FIG. 52A, the secondelectrode 5222 and the second electrode 5226 correspond to the referenceconnection pads, and the second electrode 5224 corresponds to thecomposite connection pad.

Note that a structure as shown in FIG. 52B may be employed whichincludes a third electrode 5231 over the second electrode 5222, a thirdelectrode 5232 over the second electrode 5224, and a third electrode5233 over the second electrode 5226 in the structure shown in FIG. 52A.In other words, a reference connection terminal 5234 is formed with thefirst electrode 5221, the second electrode 5222, and the third electrode5231; a composite connection terminal 5235 is formed with the firstelectrode 5223, the second electrode 5224, and the third electrode 5232;and a reference connection terminal 5236 is formed with the firstelectrode 5225, the second electrode 5226, and the third electrode 5233.In the case of the structure shown in FIG. 52B, the third electrode 5231and the third electrode 5232 correspond to the reference connectionpads, and the third electrode 5233 corresponds to the compositeconnection pad.

Note that the third electrode 5231, the third electrode 5232, and thethird electrode 5233 are formed from the same material as the pixelelectrode 5210. Preferably, the third electrode 5231, the thirdelectrode 5232, and the third electrode 5233 are formed from oxide suchas indium tin oxide (ITO) in which tin oxide is added to indium oxide,indium zinc oxide (IZO), cadmium tin oxide (CTO), zinc oxide (ZnO), ortin oxide (TO). Since the above oxide is chemically stable, it canprotect the electrode.

Alternatively, a structure as shown in FIG. 53B may be employed whichhas a semiconductor film 5311 below the first electrode 5222, asemiconductor film 5312 below the first electrode 5223, and asemiconductor film 5313 below the first electrode 5225 in the structureshown in FIG. 52A. In other words, a reference connection terminal 5314is formed with the first electrode 5221, the second electrode 5222, andthe semiconductor layer 5311; a composite connection terminal 5315 isformed with the first electrode 5223, the second electrode 5224, and thesemiconductor layer 5312; and a reference connection terminal 5316 isformed with the first electrode 5225, the second electrode 5226, and thesemiconductor layer 5313.

In addition, the connection terminal portion may have a structure asshown in FIG. 53A. In other words, a first electrode 5301, a firstelectrode 5303, and a first electrode 5305 are formed over the firstinterlayer insulating film 5207, and further, a second electrode 5302, asecond electrode 5304, and a second electrode 5306 are formed over thefirst electrode 5301, the first electrode 5303, and the first electrode5305, respectively.

In addition, the first electrode 5301, the first electrode 5303, and thefirst electrode 5305, and the second electrode 5302, the secondelectrode 5304, and the second electrode 5306 are electrically insulatedby partitions formed from the second interlayer insulating film 5209.

Note that the first electrode 5301, the first electrode 5303, and thefirst electrode 5305 are formed from the same material as the wire 5208.In addition, the second electrode 5302, the second electrode 5304, andthe second electrode 5306 are formed from the same material as the pixelelectrode 5210. Preferably, the second electrode 5302, the secondelectrode 5304, and the second electrode 5036 are formed from oxide suchas indium tin oxide (ITO) in which tin oxide is added to indium oxide,indium zinc oxide (IZO), cadmium tin oxide (CTO), zinc oxide (ZnO), ortin oxide (TO). Since the above oxide is chemically stable, it canprotect the electrode.

A reference connection terminal 5307 is formed with the first electrode5301 and the second electrode 5302. A composite connection terminal 5308is formed with the first electrode 5303 and the second electrode 5304. Areference connection terminal 5309 is formed with the first electrode5305 and the second electrode 5306. In the case of the structure asshown in FIG. 53A, the second electrode 5302 and the second electrode5306 correspond to the reference connection pads, and the secondelectrode 5304 corresponds to the composite connection pad.

The second interlayer insulating film 5209 is not necessarily provided.First, a cross section of the pixel portion is explained with referenceto FIG. 54A. Steps to formation of the wire 5208 over the firstinterlayer insulating film 5207 are similar to those shown in FIG. 52A.

In addition, an insulator 5402 is formed to cover end portions of apixel electrode 5401. For example, a positive type photosensitiveacrylic resin film can be used as the insulator 5402.

In addition, a layer 5403 containing an organic compound is formed overthe pixel electrode 5401. In addition, an opposite electrode 5404 isformed over the layer 5403 containing an organic compound.

Subsequently, a structure of the connection terminal portion isexplained. Note that a cross-sectional view of the connection terminalportion in FIG. 54A shows a section of a connection terminal in a linewidth direction.

Also in the connection terminal portion, the base film 5202 is formedover the substrate 5201, and the gate insulating film 5205 is formedthereover. However, in the connection terminal portion, the base film5202 and the gate insulating film 5205 are not necessarily formed.

Furthermore, a first electrode 5411, a first electrode 5413, and a firstelectrode 5415 are formed over the gate insulating film 5205, and asecond electrode 5412, a second electrode 5414, and a second electrode5416 are formed over the first electrode 5411, the first electrode 5413,and the first electrode 5415, respectively.

In addition, the first electrode 5411, the first electrode 5413, and thefirst electrode 5415, and the second electrode 5412, the secondelectrode 5414, and second electrode 5416 are electrically insulated bythe first interlayer insulating film 5207.

Note that the first electrode 5411, the first electrode 5413, and thefirst electrode 5415 are formed from the same material as the gateelectrode 5206. In addition, the second electrode 5412, the secondelectrode 5414, and the second electrode 5416 are formed from the samematerial as the wire 5208. Preferably, each of the second electrode5412, the second electrode 5414, and the second electrode 5416 has athree-layer structure, which may include an aluminum film over atitanium film, and a titanium film thereover.

A reference connection terminal 5421 is formed with the first electrode5411 and the second electrode 5412. A composite connection terminal 5422is formed with the first electrode 5413 and the second electrode 5414. Areference connection terminal 5423 is formed with the first electrode5415 and the second electrode 5416. In the case of the structure asshown in FIG. 54A, the second electrode 5412 and the second electrode5416 correspond to the reference connection pads, and the secondelectrode 5414 corresponds to the composite connection pad.

Note that a structure as shown in FIG. 54B may be employed whichincludes a third electrode 5431 over the second electrode 5412, a thirdelectrode 5432 over the second electrode 5414, and a third electrode5433 over the second electrode 5416 in the structure shown in FIG. 54A.In other words, a reference connection terminal 5441 is formed with thefirst electrode 5411, the second electrode 5412, and the third electrode5431; a composite connection terminal 5442 is formed with the firstelectrode 5413, the second electrode 5414, and the third electrode 5432;and a reference connection terminal 5443 is formed with the firstelectrode 5415, the second electrode 5416, and the third electrode 5433.In the case of the structure shown in FIG. 54B, the third electrode 5431and the third electrode 5432 correspond to the reference connectionpads, and the third electrode 5433 corresponds to the compositeconnection pad.

Note that the third electrode 5431, the third electrode 5432, and thethird electrode 5433 are formed from the same material as the pixelelectrode 5401. Preferably, the third electrode 5431, the thirdelectrode 5432, and the third electrode 5433 are formed from oxide suchas indium tin oxide (ITO) in which tin oxide is added to indium oxide,indium zinc oxide (IZO), cadmium tin oxide (CTO), zinc oxide (ZnO), ortin oxide (TO). Since the above oxide is chemically stable, it canprotect the electrode.

In addition, the connection terminal portion may have a structure asshown in FIG. 55A. In other words, a first electrode 5501, a firstelectrode 5503, and a first electrode 5505 are formed over the firstinterlayer insulating film 5207, and further, a second electrode 5502, asecond electrode 5504, and a second electrode 5506 are formed over thefirst electrode 5501, the first electrode 5503, and the first electrode5505, respectively.

The first electrode 5501, the first electrode 5503, and the firstelectrode 5505, and the second electrode 5502, the second electrode5504, and second electrode 5506 are electrically insulated by theinsulator 5402.

Note that the first electrode 5501, the first electrode 5503, and thefirst electrode 5505 are formed from the same material as the wire 5208.The second electrode 5502, the second electrode 5504, and the secondelectrode 5506 are formed from the same material as the pixel electrode5401. Preferably, the second electrode 5502, the second electrode 5504,and the second electrode 5506 are formed from oxide such as indium tinoxide (ITO) in which tin oxide is added to indium oxide, indium zincoxide (IZO), cadmium tin oxide (CTO), zinc oxide (ZnO), or tin oxide(TO). Since the above oxide is chemically stable, it can protect theelectrode.

A reference connection terminal 5511 is formed with the first electrode5501 and the second electrode 5502. A composite connection terminal 5512is formed with the first electrode 5503 and the second electrode 5504. Areference connection terminal 5513 is formed with the first electrode5505 and the second electrode 5506. In the case of the structure asshown in FIG. 55A, the second electrode 5502 and the second electrode5506 correspond to the reference connection pads, and the secondelectrode 5504 corresponds to the composite connection pad.

Alternatively, a structure as shown in FIG. 55B may be employed in whichthe second electrode 5502, the second electrode 5504, and the secondelectrode 5506 are not provided in the structure of FIG. 55A. In otherwords, a reference connection terminal 5521 is formed with the firstelectrode 5501. A composite connection terminal 5522 is formed with thefirst electrode 5503. A reference connection terminal 5523 is formedwith the first electrode 5505. In the case of the structure as shown inFIG. 55B, the first electrode 5501 and the first electrode 5505correspond to the reference connection pads, and the first electrode5503 corresponds to the composite connection pad.

FIGS. 56A and 56B are partial cross-sectional views of a display panelusing a transistor having a structure in which a gate electrode issandwiched between a substrate and a semiconductor layer, namely, atransistor having a bottom-gate structure in which a gate electrode islocated below a semiconductor layer, as the structure of a transistorusing polysilicon (p-Si) for its semiconductor layer.

A base film 5602 is formed over a substrate 5601. Then, a gate electrode5603 is formed over the base film 5602. As a material of the gateelectrode 5603, a metal film, or polycrystalline silicon to whichphosphorus is added can be used. Other than polycrystalline silicon,silicide that is a compound of metal and silicon may be used as well.

Then, a gate insulating film 5604 is formed to cover the gate electrode5603. The gate insulating film 5604 is formed using a silicon oxidefilm, a silicon nitride film, or the like.

Over the gate insulating film 5604, a semiconductor film is formed. Thesemiconductor film includes a channel formation region 5606 and animpurity region 5605. Note that channel doping may be performed on thechannel formation region 5606.

As the substrate, a glass substrate, a quartz substrate, a ceramicsubstrate, or the like can be used. The base film 5602 can be formedusing a single layer of aluminum nitride (AlN), silicon oxide (SiO₂),silicon oxynitride (SiO_(X)N_(Y)), or the like or a laminated layerthereof.

A first interlayer insulating film 5600 is formed to cover thesemiconductor film. A contact hole is formed in the first interlayerinsulating film 5600, through which a wire 5607 is in contact with theimpurity region 5605.

In addition, an opening 5608 is formed in the first interlayerinsulating film 5600.

A second interlayer insulating film 5609 is formed to cover the firstinterlayer insulating film 5600, the wire 5607, and the opening 5608. Apixel electrode 5610 is formed through a contact hole over the secondinterlayer insulating film 5609. Then, an insulator 5611 is formed tocover end portions of the pixel electrode 5610. For example, a positivetype photosensitive acrylic resin film can be used. Subsequently, alayer 5612 containing an organic compound and an opposite electrode 5613are formed over the pixel electrode 5610, and a light emitting element5614 is formed in a region where the layer 5612 containing an organiccompound is sandwiched between the pixel electrode 5610 and the oppositeelectrode 5613. The opening 5608 is located under the light emittingelement 5614; accordingly, in the case where light emission of the lightemitting element 5614 is extracted from the substrate side,transmittance can be improved due to the existence of the opening 5608.

Next, a structure of the connection terminal portion is explained. Notethat a cross-sectional view of the connection terminal portion in FIG.56A shows a section of a connection terminal in a line width direction.

Also in the connection terminal portion, the base film 5602 is formedover the substrate 5601, and the gate insulating film 5604 is formedthereover. However, in the connection terminal portion, the base film5602 and the gate insulating film 5604 are not necessarily formed.

Furthermore, a semiconductor film 5615, a semiconductor film 5617, and asemiconductor film 5619 are formed over the gate insulating film 5604,and further, a first conductive film 5616, a first conductive film 5618,and a first conductive film 5620 are formed over the semiconductor film5615, the semiconductor film 5617, and the semiconductor film 5619,respectively.

In addition, the semiconductor film 5615, the semiconductor film 5617,and the semiconductor film 5619, and the first conductive film 5616, thefirst conductive film 5618, and the first conductive film 5620 areelectrically insulated by partitions formed from the first interlayerinsulating film 5600 and the second interlayer insulating film 5609.

Note that the semiconductor film 5615, the semiconductor film 5617, andthe semiconductor film 5619 are formed from the same material as thesemiconductor layer of the transistor. In addition, the first conductivefilm 5616, the first conductive film 5618, and the first conductive film5620 are formed from the same material as the wire 5607.

A reference connection terminal 5621 is formed with the semiconductorfilm 5615 and the first conductive film 5616. A composite connectionterminal 5622 is formed with the semiconductor film 5617 and the firstconductive film 5618. A reference connection terminal 5623 is formedwith the semiconductor film 5619 and the first conductive film 5620. Inthe case of the structure as shown in FIG. 56A, the first conductivefilm 5616 and the first conductive film 5620 correspond to the referenceconnection pads, and the first conductive film 5618 corresponds to thecomposite connection pad.

Note that a structure as shown in FIG. 56B may be employed whichincludes a second conductive film 5631 over the first conductive film5616, a second conductive film 5632 over the first conductive film 5618,and a second conductive film 5633 over the first conductive film 5620 inthe structure shown in FIG. 56A. In other words, a reference connectionterminal 5641 is formed with the semiconductor film 5615, the firstconductive film 5616, and the second conductive film 5631; a compositeconnection terminal 5642 is formed with the semiconductor film 5617, thefirst conductive film 5618, and the second conductive film 5632; and areference connection terminal 5643 is formed with the semiconductor film5619, the first conductive film 5620, and the second conductive film5633. In the case of the structure as shown in FIG. 56B, the secondconductive film 5631 and the second conductive film 5632 correspond tothe reference connection pads, and the second conductive film 5633corresponds to the composite connection pad.

Note that the second conductive film 5631, the second conductive film5632, and the second conductive film 5633 are formed from the samematerial as the pixel electrode 5610. Preferably, the second conductivefilm 5631, the second conductive film 5632, and the second conductivefilm 5633 are formed from oxide such as indium tin oxide (ITO) in whichtin oxide is added to indium oxide, indium zinc oxide (IZO), cadmium tinoxide (CTO), zinc oxide (ZnO), or tin oxide (TO). Since the above oxideis chemically stable, it can protect the electrode.

Alternatively, a structure as shown in FIG. 57B may be employed in whichthe semiconductor layer 5615, the semiconductor layer 5617, and thesemiconductor layer 5619 are not provided in the structure of FIG. 56B.In other words, a reference connection terminal 5711 is formed with thefirst conductive film 5616 and the second conductive film 5631. Acomposite connection terminal 5712 is formed with the first conductivefilm 5618 and the second conductive film 5632. A reference connectionterminal 5713 is formed with the first conductive film 5620 and thesecond conductive film 5633. In the case of the structure as shown inFIG. 57B, the second conductive film 5631 and the second conductive film5633 correspond to the reference connection pads, and the secondconductive film 5632 corresponds to the composite connection pad.

In addition, the connection terminal portion may have a structure asshown in FIG. 57A. In other words, a first conductive film 5701, a firstconductive film 5703, and a first conductive film 5705 are formed overthe first interlayer insulating film 5600, and further, a secondconductive film 5702, a second conductive film 5704, and a secondconductive film 5706 are formed over the first conductive film 5701, thefirst conductive film 5703, and the first conductive film 5705,respectively.

In addition, the first conductive film 5701, the first conductive film5703, and the first conductive film 5705, and the second conductive film5702, the second conductive film 5704, and the second conductive film5706 are electrically insulated by partitions formed from the secondinterlayer insulating film 5609.

Note that the first conductive film 5701, the first conductive film5703, and the first conductive film 5705 are formed from the samematerial as the wire 5607. In addition, the second conductive film 5702,the second conductive film 5704, and the second conductive film 5706 areformed from the same material as the pixel electrode 5610. Preferably,the second conductive film 5702, the second conductive film 5704, andthe second conductive film 5706 are formed from oxide such as indium tinoxide (ITO) in which tin oxide is added to indium oxide, indium zincoxide (IZO), cadmium tin oxide (CTO), zinc oxide (ZnO), or tin oxide(TO). Since the above oxide is chemically stable, it can protect theelectrode.

A reference connection terminal 5707 is formed with the first conductivefilm 5701 and the second conductive film 5702. A composite connectionterminal 5708 is formed with the first conductive film 5703 and thesecond conductive film 5704. A reference connection terminal 5709 isformed with the first conductive film 5705 and the second conductivefilm 5706. In the case of the structure as shown in FIG. 57A, the secondconductive film 5702 and the second conductive film 5706 correspond tothe reference connection pads, and the second conductive film 5704corresponds to the composite connection pad.

Subsequently, the case of using an amorphous silicon (a-Si:H) film as asemiconductor layer of a transistor is explained.

FIG. 58A is a cross-sectional view of a top-gate transistor usingamorphous silicon for its semiconductor layer. As shown in FIG. 58A, abase film 5802 is formed over a substrate 5801. Further, a pixelelectrode 5803 is formed over the base film 5802.

As the substrate, a glass substrate, a quartz substrate, a ceramicsubstrate, or the like can be used. The base film 5802 can be formedusing a single layer of aluminum nitride (MN), silicon oxide (SiO₂),silicon oxynitride (SiO_(X)N_(Y)), or the like or a laminated layerthereof.

A wire 5804 is formed over the base film 5802, and an end portion of thepixel electrode 5803 is covered with the wire 5804. Over the wire 5804,an n-type semiconductor layer 5806 having n-type conductivity is formed.In addition, a semiconductor layer 5805 is formed over the n-typesemiconductor layer 5806 and the base film 5802. Note that thissemiconductor layer is formed using an amorphous semiconductor film suchas amorphous silicon (a-Si:H) film or a microcrystalline semiconductor(μ-Si:H) film. Then, a gate insulating film 5807 is formed over thesemiconductor layer 5805. Note that a silicon oxide film, a siliconnitride film, or the like is used as the gate insulating film 5807.

Over the gate insulating film 5807, a gate electrode 5808 is formed. Inaddition, an insulator 5809 is formed to cover end portions of the pixelelectrode 5803 and a transistor 5812.

Over the insulator 5809 and the pixel electrode 5803 located in anopening of the insulator 5809, a layer 5810 containing an organiccompound and an opposite electrode 5811 are formed. A light emittingelement 5813 is formed in a region where the layer 5810 containing anorganic compound is sandwiched between the pixel electrode 5803 and theopposite electrode 5811.

Next, a structure of a connection terminal portion is explained. Notethat a cross-sectional view of a connection terminal portion in FIG. 58Ashows a section of a connection terminal in a line width direction.

Also in the connection terminal portion, the base film 5802 is formedover the substrate 5801. However, in the connection terminal portion,the base film 5802 is not necessarily formed.

Furthermore, a first conductive film 5814, a first conductive film 5816,and a first conductive film 5818 are formed over the base film 5802, andfurther, a second conductive film 5815, a second conductive film 5817,and a second conductive film 5819 are formed over the first conductivefilm 5814, the first conductive film 5816, and the first conductive film5818, respectively.

In addition, the first conductive film 5814, the first conductive film5816, and the first conductive film 5818, and the second conductive film5815, the second conductive film 5817, and the second conductive film5819 are electrically insulated by the insulator 5809.

Note that the first conductive film 5814, the first conductive film5816, and the first conductive film 5818 are formed from the samematerial as the wire 5804. The second conductive film 5815, the secondconductive film 5817, and the second conductive film 5819 are formedfrom the same material as the gate electrode 5808.

A reference connection terminal 5820 is formed with the first conductivefilm 5814 and the second conductive film 5815. A composite connectionterminal 5821 is formed with the first conductive film 5816 and thesecond conductive film 5817. A reference connection terminal 5822 isformed with the first conductive film 5818 and the second conductivefilm 5819. In the case of the structure as shown in FIG. 58A, the secondconductive film 5815 and the second conductive film 5819 correspond tothe reference connection pads, and the second conductive film 5817corresponds to the composite connection pad.

Alternatively, a structure as shown in FIG. 58B may be employed whichincludes a third conductive film 5823 below the first conductive film5814, a third conductive film 5824 below the first conductive film 5816,and a third conductive film 5825 below the first conductive film 5818 inthe structure of FIG. 58A. In other words, the reference connectionterminal 5820 is formed with the first conductive film 5814, the secondconductive film 5815, and the third conductive film 5823; the compositeconnection terminal 5821 is formed with the first conductive film 5816,the second conductive film 5817, and the third conductive film 5824; andthe reference connection terminal 5822 is formed with the conductivefilm 5818, the second conductive film 5819, and the third conductivefilm 5825.

FIGS. 59A and 59B are partial cross-sectional views of a display panelprovided with a bottom-gate transistor using amorphous silicon for itssemiconductor layer.

A base film 5902 is formed over a substrate 5901. Over the base film5902, a gate electrode 5903 is formed. As a material of the gateelectrode 5903, polycrystalline silicon to which phosphorus is added canbe used. Other than polycrystalline silicon, silicide that is a compoundof metal and silicon may be used as well.

Then, a gate insulating film 5904 is formed to cover the gate electrode5903. The gate insulating film 5904 is formed using a silicon oxidefilm, a silicon nitride film, or the like.

A semiconductor layer 5905 is formed over the gate insulating film 5904.

As the substrate, a glass substrate, a quartz substrate, a ceramicsubstrate, or the like can be used. The base film 5902 can be formedusing a single layer of aluminum nitride (AlN), silicon oxide (SiO₂),silicon oxynitride (SiO_(X)N_(Y)), or the like or a laminated layerthereof.

An n-type semiconductor layer 5906 having n-type conductivity is formedover the semiconductor layer 5905.

A wire 5907 is formed over the n-type semiconductor layer 5906.

One end portion of the wire 5907 is extended, and a pixel electrode 5908is formed on the extended wire 5907.

An insulator 5909 is formed to cover end portions of the pixel electrode5908 and a transistor 5912.

Then, a layer 5910 containing an organic compound and an oppositeelectrode 5911 are formed over the pixel electrode 5908 and theinsulator 5909. A light emitting element 5913 is formed in a regionwhere the layer 5910 containing an organic compound is sandwichedbetween the pixel electrode 5908 and the opposite electrode 5911.

Next, a structure of a connection terminal portion is explained. Notethat a cross-sectional view of a connection terminal portion in FIG. 59Ashows a section of a connection terminal in a line width direction.

Also in the connection terminal portion, the base film 5902 is formedover the substrate 5901. However, in the connection terminal portion,the base film 5902 is not necessarily formed.

Furthermore, a first conductive film 5914, a first conductive film 5915,and a first conductive film 5916 are formed over the base film 5902.

In addition, the first conductive film 5914, the first conductive film5915, and the first conductive film 5916 are electrically insulated bythe insulator 5909.

Note that the first conductive film 5914, the first conductive film5915, and the first conductive film 5916 are formed from the samematerial as the wire 5907.

A reference connection terminal 5917 is formed with the first conductivefilm 5914. A composite connection terminal 5918 is formed with the firstconductive film 5915. A reference connection terminal 5919 is formedwith the first conductive film 5916. In the case of the structure asshown in FIG. 59A, the first conductive film 5914 and the firstconductive film 5916 correspond to the reference connection pads, andthe first conductive film 5915 corresponds to the composite connectionpad.

Alternatively, a structure as shown in FIG. 59B may be employed whichincludes a second conductive film 5920 over the first conductive film5914, a second conductive film 5921 over the first conductive film 5915,and a second conductive film 5922 over the first conductive film 5916 inthe structure shown in FIG. 59A. In other words, a reference connectionterminal 5923 is formed with the first conductive film 5914 and thesecond conductive film 5920; a composite connection terminal 5924 isformed with the first conductive film 5915 and the second conductivefilm 5921; and a reference connection terminal 5925 is formed with thefirst conductive film 5916 and the second conductive film 5922.

Note that FIGS. 59A and 59B show inverted-staggered channel-etch typetransistors; however, a channel protective type transistor may be used.The case of a channel protective type transistor is explained withreference to FIGS. 60A and 60B.

A channel protective type transistor 6002 shown in FIGS. 60A and 60B isdifferent from the channel-etch type transistor 5912 shown in FIGS. 59Aand 59B in that an insulator 6001 serving as an etching mask is providedover the channel formation region in the semiconductor layer 5905. Theother common components are denoted by the common reference numerals.

By using an amorphous semiconductor film as a semiconductor layer (suchas a channel formation region, a source region, and a drain region) of atransistor included in the pixel of the invention, manufacturing costcan be reduced.

Note that a display panel to which the present invention can be appliedis not limited to those described above.

Embodiment Mode 7

In this embodiment mode, a structure of a composite connection terminal,which is different from that in Embodiment Mode 1, is explained.

First, a first structure of this embodiment mode is explained withreference to FIGS. 39A and 39B. A connection pad 3901 a, a plurality ofconnection pads 3902, and a connection pad 3901 b are arranged equallyspaced in a connection terminal portion over a substrate 101. Inaddition, the line widths of these connection pads are alsoapproximately equal to each other.

An electrode 3903 is formed below the connection pads 3902 with aninsulating film therebetween. The electrode 3903 is formed from theconnection pad 3901 a to the connection pad 3901 b. Then, the connectionpad 3901 a is electrically connected to the electrode 3903 through acontact hole 3904 a, and the connection pad 3901 b is electricallyconnected to the electrode 3903 through a contact hole 3904 b. Thus, theconnection pad 3901 a and the connection pad 3901 b are electricallyconnected to each other. A composite connection terminal is formed withthe connection pad 3901 a, the connection pad 3901 b, and the electrode3903. Further, a portion where the composite connection terminal isconnected to an FPC terminal is the connection pad 3901 a and theconnection pad 3901 b.

Note that in FIG. 39, connection pads on both ends of a connectionterminal portion are electrically connected to each other, with which acomposite connection terminal is formed; however, the present inventionis not limited thereto. In other words, a composite connection terminalcan be formed by electrically connecting any connection pads in theconnection terminal portion to each other. Accordingly, the number ofconnection pads to be electrically connected is not limited to two, andit may be three or more. By increasing the number, a connection areawith an FPC pad can be enlarged; therefore, contact resistance can bedecreased.

In accordance with this structure, connection pads are electricallyconnected to each other in a lower layer of the connection terminalportion. Therefore, the connection between spaced-apart connection padsis allowed without extending a wire inside a portion surrounded by asealing region 901.

Note that this structure can be combined with various structures of theconnection terminal portions described in Embodiment Mode 2. An exampleis shown in FIG. 61.

In FIG. 61, a composite connection pad 6101 a, a composite connectionpad 6101 b, a composite connection pad 6102, and a reference connectionpad 6103 are arranged equally spaced in a connection terminal portionover a substrate 101.

An electrode 6104 is formed below the composite connection pad 6101 aand the composite connection pad 6101 b with an insulating filmtherebetween. The electrode 6104 is formed from the composite connectionpad 6101 a to the composite connection portion 6101 b. Then, thecomposite connection pad 6101 a is electrically connected to theelectrode 6104 through a contact hole 6105 a, and the compositeconnection pad 6101 b is electrically connected to the electrode 6104through a contact hole 6105 b. Thus, the composite connection pad 6101 aand the composite connection pad 6101 b are electrically connected toeach other. A composite connection terminal is formed with the compositeconnection pad 6101 a, the composite connection pad 6101 b, and theelectrode 6104. Further, a portion where the composite connectionterminal is connected to an FPC terminal is the composite connection pad6101 a and the composite connection pad 6101 b.

Note that in this case, the width of the contact hole 6105 a can be madelarger than the line width of the reference connection pad 6103.Therefore, contact resistance can be decreased.

Note that in FIG. 61, composite connection pads on both ends of theconnection terminal portion are electrically connected to each other,with which a composite connection terminal is formed; however, thepresent invention is not limited thereto. In other words, a compositeconnection terminal can be formed by electrically connecting anyconnection pads in the connection terminal portion to each other.Accordingly, the number of connection pads to be electrically connectedis not limited to two, and it may be three or more. By increasing thenumber, a connection area with an FPC pad can be enlarged; therefore,contact resistance can be decreased.

Further, although composite connection pads are connected to each other,a composite connection terminal may be formed by electrically connectinga composite connection pad and a reference connection pad to each other.

In accordance with this structure, connection pads are electricallyconnected in a lower layer of a connection terminal portion. Therefore,the connection between spaced-apart connection pads is allowed withoutextending a wire inside a portion surrounded by a sealing region 901.

Subsequently, a second structure of this embodiment mode is explainedwith reference to FIG. 37. A connection pad 3701 a, a plurality ofconnection pads 3702, and a connection pad 3701 b are arranged equallyspaced in a connection terminal portion over a substrate 101. Inaddition, the line widths of these connection pads are alsoapproximately equal to each other.

The connection pad 3701 a and the connection pad 3701 b are connected bya wire 3703 formed at the periphery of the substrate 101 in theconnection terminal portion. Note that the wire 3703 is formed of aconductive film continuous with the connection pad 3701 a and theconnection pad 3701 b; therefore, the wire 3703, the connection pad 3701a, and the connection pad 3701 b are electrically connected to eachother without a contact hole. Accordingly, a composite connectionterminal is formed with the connection pad 3701 a, the connection pad3701 b, and the wire 3703. Further, a portion where the compositeconnection terminal is connected to an FPC terminal is the connectionpad 3701 a and the connection pad 3701 b.

Note that in FIG. 37, connection pads on both ends of a connectionterminal portion are electrically connected to each other, with which acomposite connection terminal is formed; however, the present inventionis not limited thereto. In other words, a composite connection terminalcan be formed by electrically connecting any connection pads in theconnection terminal portion to each other. Accordingly, the number ofconnection pads to be electrically connected is not limited to two, andit may be three or more. By increasing the number, a connection areawith an FPC pad can be enlarged; therefore, contact resistance can bedecreased.

In accordance with this structure, connection pads are connected to eachother without a contact hole; therefore, the connection betweenspaced-apart connection pads is allowed without causing an increase incontact resistance. Thus, resistance can be decreased.

Note that this structure can be combined with various structures of theconnection terminal portions described in Embodiment Mode 2. An exampleis shown in FIG. 38.

In FIG. 38, a composite connection pad 3801 a, a composite connectionpad 3801 b, a composite connection pad 3802, and a reference connectionpad 3803 are arranged equally spaced in a connection terminal portionover a substrate 101.

The composite connection pad 3801 a and the composite connection pad3801 b are connected to each other by a wire 3804 formed at theperiphery of the substrate 101 in a connection terminal portion. Notethat the wire 3804 is formed of a conductive film continuous with thecomposite connection pad 3801 a and the composite connection pad 3801 b;therefore, the wire 3804, the composite connection pad 3801 a, and thecomposite connection pad 3801 b are electrically connected to each otherwithout a contact hole. Accordingly, a composite connection terminal isformed with the composite connection pad 3801 a, the compositeconnection pad 3801 b, and the wire 3804. Further, a portion where thecomposite connection terminal is connected to an FPC terminal is thecomposite connection pad 3801 a and the composite connection pad 3801 b.

Note that in FIG. 38, connection pads on both ends of the connectionterminal portion are electrically connected to each other, with which acomposite connection terminal is formed; however, the present inventionis not limited thereto. In other words, a composite connection terminalcan be formed by electrically connecting any composite connection padsin a connection terminal portion to each other. Accordingly, the numberof connection pads to be electrically connected is not limited to two,and it may be three or more. Alternatively, a composite connection padand a reference connection pad may be electrically connected to eachother with a wire provided at the periphery of a substrate. Note that,by increasing the number, a connection area with an FPC pad can beenlarged; therefore, contact resistance can be decreased.

Embodiment Mode 8

In this embodiment mode, a structure which enables further improvementin defective display of a display device is explained.

In the structure of this embodiment mode, a current source circuit inperipheral driver circuits (a scan line driver circuit, a signal linedriver circuit, and the like) and a wire connecting the current sourcecircuit and a current source are not overlapped with an oppositeelectrode.

First, a first structure of this embodiment mode is shown in FIG. 27.Note that components in common with FIG. 13 are denoted by commonreference numerals, and explanation thereof is omitted. In the structureshown in FIG. 27, the signal line driver circuit 104 includes a latchcircuit 2701 and a shift register 2702. The latch circuit 2701 isarranged at a more distant location from the pixel portion 106 than theshift register 2702. For effective use of a display panel area, thedistance between the signal line driver circuit 104 and the pixelportion 106 is short. Therefore, the opposite electrode 202 whichextends out of the pixel portion 106 partially overlaps the shiftregister 2702. However, the latch circuit 2701 including the currentsource, the current source circuit, the wire for connecting them, andthe like is not overlapped with the opposite electrode 202.

With such a structure, defective display due to the influence ofparasitic capacitance formed with the wire and the opposite electrode202 can be prevented while effectively utilizing a display panel area.

This is because the time to hold a video signal inputted to the latchcircuit 2701 in each stage of a latch circuit is shorter than the timeto write a video signal to a pixel from the latch circuit 2701;therefore, if a signal current corresponding to the video signal issmall, the influence of parasitic capacitance grows, and the videosignal is not normally written to the latch circuit 2701.

Here, an example of the configuration of the signal line driver circuit104 is shown in FIG. 42. The shift register 2702 includes a plurality offlip-flops 4201 and flip-flops 4202. A clock signal (CLK) and aninverted clock signal (CLKB) are inputted to the shift register 2702.Then, a start pulse (S_SP) is inputted to the flip-flop 4201 of a firststage of the shift register 2702. Then, as for a pulse outputted fromthe flip-flop 4202 of a second stage, a start pulse is delayed for onepulse. In other words, a pulse inputted to the flip-flop 4201 is delayedfor one pulse when outputted from the flip-flop 4202; therefore, eachoutput from the flip-flop 4202 is delayed for one pulse. This serves asa sampling pulse determining the timing at which a video signal (VideoData) is held.

In addition, the latch circuit 2701 includes a write selection switch4203 a, a write selection switch 4203 b, a sampling switch 4204 a, asampling switch 4204 b, a current source circuit 4205 a, a currentsource circuit 4205 b, a read selection switch 4206 a, and a readselection switch 4206 b in accordance with each signal line.

One of the write selection switch 4203 a and the write selection switch4203 b is turned on, and the other is turned off. When the writeselection switch 4203 a is turned on, the write selection switch 4203 bis turned off and the current source circuit 4205 a is selected as acurrent source circuit for writing a video signal. In other words, thesampling switch 4204 a is turned on in accordance with the timing atwhich the sampling pulse is inputted to the latch circuit 2701, and acurrent corresponding to the video signal is written to the currentsource circuit 4205 a. In the same manner, when the write selectionswitch 4203 b is turned on, the write selection switch 4203 a is turnedoff and the current source circuit 4205 b is selected as a currentsource circuit for writing a video signal. In other words, the samplingswitch 4204 b is turned on in accordance with the timing at which thesampling pulse is inputted to the latch circuit 2701, and a currentcorresponding to the video signal is written to the current sourcecircuit 4205 b.

In addition, when the write selection switch 4203 a is turned on, theread selection switch 4206 b is turned on and the read selection switch4206 a is turned off. Then, the current corresponding to the videosignal written to the current source circuit 4205 b is outputted to thesignal line. In the same manner, when the write selection switch 4203 bis turned on, the read selecting switch 4206 a is turned on and the readselection switch 4206 b is turned off. Then, the current correspondingto the video signal written to the current source circuit 4205 a isoutputted to the signal line.

Here, parasitic capacitance is generated when a video line 4207 to whichthe video signal (Video Data) is inputted is overlapped with theopposite electrode. When a current value corresponding to the videosignal is small, current flows to the parasitic capacitance, whichresults in insufficient video signal writing to the current sourcecircuit. Consequently, defective display is caused.

However, defective display can be prevented by employing the structureof this embodiment mode as shown in FIG. 27 because the oppositeelectrode 202 does not overlap the latch circuit 2701 even if effectiveuse of the display panel area is attempted.

Note that any of the structures as shown in FIGS. 43A to 43C can beapplied to the current source circuit. A current source circuit of FIG.43A includes a switch 4304, a transistor 4302, and a capacitor 4303. Inaddition, writing to the current source circuit is performed by acurrent source 4301. A current source circuit of FIG. 43B includes aswitch 4313, a transistor 4311, and a capacitor 4312. In addition,writing to the current source circuit is performed by the current source4301. A current source circuit of FIG. 43C includes a switch 4324, atransistor 4321, a transistor 4322, a capacitor 4323, and a switch 4325.In addition, writing to the current source circuit is performed by thecurrent source 4301.

Next, a second structure of this embodiment mode is shown in FIG. 28.Note that components in common with FIG. 14 are denoted by commonreference numerals, and explanation thereof is omitted. Also in thisstructure, the signal line driver circuit 104 includes the latch circuit2701 and the shift register 2702. The latch circuit 2701 is arranged ata more distant location from the pixel portion 106 than the shiftregister 2702. For effective use of a display panel area, the distancebetween the signal line driver circuit 104 and the pixel portion 106 isshort. Therefore, the opposite electrode 202 which extends out of thepixel portion 106 partially overlaps the shift register 2702. However,the latch circuit 2701 including a current source, a current sourcecircuit, a wire for connecting them, and the like is not overlapped withthe opposite electrode 202.

In this structure, the wire 1403 is connected to the opposite electrode202 through the contact hole 1404 in the shift register 2702.

Next, a third structure of this embodiment mode is shown in FIG. 29.Note that components in common with FIG. 15 are denoted by commonreference numerals, and explanation thereof is omitted. Also in thisstructure, the signal line driver circuit 104 includes the latch circuit2701 and the shift register 2702. The latch circuit 2701 is arranged ata more distant location from the pixel portion 106 than the shiftregister 2702. For effective use of a display panel area, the distancebetween the signal line driver circuit 104 and the pixel portion 106 isshort. Therefore, the opposite electrode 202 which extends out of thepixel portion 106 partially overlaps the shift register 2702. However,the latch circuit 2701 including a current source, a current sourcecircuit, a wire for connecting them, and the like is not overlapped withthe opposite electrode 202.

In this structure, the latch circuit 2701 is arranged on the sideopposite to the connection terminal 201 to which a signal or power issupplied, with the pixel portion 106 therebetween; thus, a wire that isa cause of parasitic capacitance generation does not extend across thelatch circuit 2701. Therefore, defective display can further beprevented.

Subsequently, a fourth structure of this embodiment mode is shown inFIG. 30. Note that components in common with FIG. 16 are denoted bycommon reference numerals, and explanation thereof is omitted. Also inthis structure, the signal line driver circuit 104 includes the latchcircuit 2701 and the shift register 2702. The latch circuit 2701 isarranged at a more distant location from the pixel portion 106 than theshift register 2702. For effective use of a display panel area, thedistance between the signal line driver circuit 104 and the pixelportion 106 is short. Therefore, the opposite electrode 202 whichextends out of the pixel portion 106 partially overlaps the shiftregister 2702. However, the latch circuit 2701 including a currentsource, a current source circuit, a wire for connecting them, and thelike is not overlapped with the opposite electrode 202. Therefore,defective display can be prevented.

Subsequently, a fifth structure of this embodiment mode is shown in FIG.31. Note that components in common with FIG. 17 are denoted by commonreference numerals, and explanation thereof is omitted. Also in thisstructure, the signal line driver circuit 104 includes the latch circuit2701 and the shift register 2702. The latch circuit 2701 is arranged ata more distant location from the pixel portion 106 than the shiftregister 2702. For effective use of a display panel area, the distancebetween the signal line driver circuit 104 and the pixel portion 106 isshort. Therefore, the opposite electrode 202 which extends out of thepixel portion 106 partially overlaps the shift register 2702. However,the latch circuit 2701 including a current source, a current sourcecircuit, a wire for connecting them, and the like is not overlapped withthe opposite electrode 202. Therefore, defective display can beprevented.

Subsequently, a sixth structure of this embodiment mode is shown in FIG.32. Note that components in common with FIG. 18 are denoted by commonreference numerals, and explanation thereof is omitted. Also in thisstructure, the signal line driver circuit 104 includes the latch circuit2701 and the shift register 2702. The latch circuit 2701 is arranged ata more distant location from the pixel portion 106 than the shiftregister 2702. For effective use of a display panel area, the distancebetween the signal line driver circuit 104 and the pixel portion 106 isshort. Therefore, the opposite electrode 202 which extends out of thepixel portion 106 partially overlaps the shift register 2702. However,the latch circuit 2701 including a current source, a current sourcecircuit, a wire for connecting them, and the like is not overlapped withthe opposite electrode 202. Therefore, defective display can beprevented.

Subsequently, a seventh structure of this embodiment mode is shown inFIG. 33. Note that components in common with FIG. 19 are denoted bycommon reference numerals, and explanation thereof is omitted. Also inthis structure, the signal line driver circuit 104 includes the latchcircuit 2701 and the shift register 2702. The latch circuit 2701 isarranged at a more distant location from the pixel portion 106 than theshift register 2702. For effective use of a display panel area, thedistance between the signal line driver circuit 104 and the pixelportion 106 is short. Therefore, the opposite electrode 202 whichextends out of the pixel portion 106 partially overlaps the shiftregister 2702. However, the latch circuit 2701 including a currentsource, a current source circuit, a wire for connecting them, and thelike is not overlapped with the opposite electrode 202. Therefore,defective display can be prevented.

Subsequently, an eighth structure of this embodiment mode is shown inFIG. 34. Note that components in common with FIG. 20 are denoted bycommon reference numerals, and explanation thereof is omitted. Also inthis structure, the signal line driver circuit 104 includes the latchcircuit 2701 and the shift register 2702. The latch circuit 2701 isarranged at a more distant location from the pixel portion 106 than theshift register 2702. For effective use of a display panel area, thedistance between the signal line driver circuit 104 and the pixelportion 106 is short. Therefore, the opposite electrode 202 whichextends out of the pixel portion 106 partially overlaps the shiftregister 2702. However, the latch circuit 2701 including a currentsource, a current source circuit, a wire for connecting them, and thelike is not overlapped with the opposite electrode 202. Therefore,defective display can be prevented.

Embodiment 1

In the embodiment, a favorable magnitude relation between the line widthof a reference connection pad, the line width of a composite connectionpad, the connection pitch, the line width of an FPC pad, and the FPCpitch described in Embodiment Mode 1 is explained with reference toFIGS. 35A to 35C.

FIG. 35A shows that a substrate 101 provided with a circuit is connectedto an FPC 103. A partial enlarged diagram of a region surrounded by adotted line 3501 is shown in FIG. 35B. In addition, a cross sectionthereof is shown in FIG. 35C.

First, explanation is made with reference to FIG. 35C. Connection pads(a reference connection pad 112 and a composite connection pad 113) areformed over the substrate 101, and a partition 114 is formed eachbetween the connection pads. The partition 114 has an insulatingproperty and maintains the insulation between the connection pads. Theconnection pads (the reference connection pad 112 and the compositeconnection pad 113) are connected to respective corresponding FPC pads111 through an anisotropic conductive film 411. Note that the structurein the case where the composite connection pad 113 is connected to twoFPC pads 111 is described here; however, the invention is not limitedthereto. In addition, a conductive particle 421 may be mixed in theanisotropic conductive film 411. According to this, contact resistancecan be decreased.

In the case where misalignment in a line width direction of the pad isnot caused in attachment of the FPC 103 and the substrate 101, thecentral axis of the reference connection pad 112 is aligned with thecentral axis of the FPC pad 111, which is as shown in FIGS. 35B and 35C.

Subsequently, explanation is made with reference to FIG. 35B. A line3502 indicates an edge of the FPC.

A line width L1 of the reference connection pad 112 is formed to besmaller than a connection pitch L3. A line width L2 of the FPC pad 111is formed to be larger than an FPC pitch L4. Furthermore, the line widthL1 of the reference connection pad 112 is formed to be smaller than theline width L2 of the FPC pad 111. In other words, by forming each pad tosatisfy the conditions L1<L3, L2>L4, and L1<L2, electrical connectionbetween corresponding pads is allowed and generation of a short circuitwith an adjacent pad can be reduced, even if slight misalignment in aline width direction of the pad is caused in attachment of the FPC 103and the substrate 101.

Furthermore, according to this structure, a line width L5 of thecomposite connection pad 113 is approximately equal to the total of theline width L2 of the PFC pad 111, the line width L1 of the referenceconnection pad 112, and the FPC pitch L4. In other words, L5=L2+L1+ L4is satisfied. In addition, the line width of a connection region betweenthe composite connection pad 113 and two FPC pads 111 is L2+L1. Then, L2is larger than L1; therefore, the connection area between the compositeconnection pad 113 and the two FPC pads 111 is twice or more theconnection area between the reference connection pad 112 and the FPC pad111. Accordingly, contact resistance of the composite connection pad 113can be decreased drastically. Note that, also in the case of connectingthe composite connection pad 113 to three or more FPC pads 111, aconnection area is drastically enlarged in the same manner; thus,contact resistance can be decreased.

Embodiment 2

In this embodiment, a structure of a display panel in the case of usinga light emitting element as a display element is explained.

In this embodiment, a display panel applicable to a display device ofthe present invention is explained with reference to FIGS. 66A and 66B.Note that FIG. 66A is a top view showing a display panel, and FIG. 66Bis a cross-sectional view of FIG. 66A taken along line a-a′. The displaypanel includes a signal line driver circuit 6601, a pixel portion 6602,a second scan line driver circuit 6603, and a first scan line drivercircuit 6606 which are indicated by dotted lines. It also includes asealing substrate 6604 and a sealant 6605, and a portion surrounded bythe sealant 6605 is a space 6607.

Note that a wire 6608 is a wire for transmitting a signal to be inputtedto the second scan line driver circuit 6603, the first scan line drivercircuit 6606, and the signal line driver circuit 6601 and receives avideo signal, a clock signal, a start signal, and the like through anFPC (flexible printed circuit) 6609 that serves as an external inputterminal. An IC chip (a semiconductor chip provided with a memorycircuit, a buffer circuit, or the like) 6619 is mounted by COG (Chip OnGlass) or the like at the junction of the FPC 6609 and the displaypanel. Note that only the FPC is shown here; however, a printed wiringboard (PWB) may be attached to the FPC. The display device in thisspecification includes not only a display panel itself but also adisplay panel with an FPC or a PWB attached thereto. In addition, italso includes a display panel on which an IC chip or the like ismounted.

Next, a cross-sectional structure is explained with reference to FIG.66B. The pixel portion 6602 and its peripheral driver circuits (thesecond scan line driver circuit 6603, the first scan line driver circuit6606, and the signal line driver circuit 6601) are formed over asubstrate 6610; here, the signal line driver circuit 6601 and the pixelportion 6602 are shown.

Note that as the signal line driver circuit 6601, a CMOS circuit isformed using an n-channel TFT 6620 and a p-channel TFT 6621. In thisembodiment, the display panel in which the peripheral driver circuitsare integrated over the substrate is described; however, the inventionis not limited to this. All or part of the peripheral driver circuitsmay be formed on an IC chip or the like and mounted by COG or the like.

The pixel portion 6602 includes a plurality of circuits each forming apixel which includes a TFT 6611 and a TFT 6612. Note that a sourceelectrode of the TFT 6612 is connected to a first electrode 6613. Aninsulator 6614 is formed to cover end portions of the first electrode6613. Here, a positive type photosensitive acrylic resin film is used.

The insulator 6614 is formed to have a curved surface with a curvatureat an upper end portion or a lower end portion thereof in order to makethe coverage favorable. For example, in the case of using positive typephotosensitive acrylic as a material of the insulator 6614, theinsulator 6614 is preferably formed to have a curved surface with acurvature radius (0.2 μm to 3 μm) only at the upper end portion. Eithera negative type which becomes insoluble in an etchant by lightirradiation or a positive type which becomes soluble in an etchant bylight irradiation can be used as the insulator 6614.

A layer 6616 containing an organic compound and a second electrode 6617are formed over the first electrode 6613. Here, a material having a highwork function is preferably used as a material used for the firstelectrode 6613 which functions as an anode. For example, the firstelectrode 6613 can be formed using a single-layer film such as an ITO(indium tin oxide) film, an indium zinc oxide film (IZO) film, atitanium nitride film, a chromium film, a tungsten film, a Zn film, or aPt film; a laminated layer of a titanium nitride film and a filmcontaining aluminum as its main component; a three-layer structure of atitanium nitride film, a film containing aluminum as its main component,and a titanium nitride film; or the like. When the first electrode 6613has a laminated structure, it can have low resistance as a wire and forma favorable ohmic contact. Further, the first electrode can function asan anode.

In addition, the layer 6616 containing an organic compound is formed byan evaporation method using an evaporation mask or an ink-jet method. Ametal complex belonging to Group 4 of the Periodic Table is used forpart of the layer 6616 containing an organic compound, and besides, amaterial which can be used in combination may be either a low molecularmaterial or a high molecular material. In addition, as a material usedfor the layer containing an organic compound, a single layer or alaminated layer of an organic compound is often used generally. Inaddition, this embodiment also includes a structure in which aninorganic compound is used for part of the film formed of an organiccompound. Moreover, a known triplet material can also be used.

As a material used for the second electrode (cathode) 6617 which isformed over the layer 6616 containing an organic compound, a materialhaving a low work function (Al, Ag, Li, Ca, or an alloy thereof such asMgAg, MgIn, AlLi, CaF₂, or Ca₃N₂) may be used. In the case where lightgenerated in the layer 6616 containing an organic compound istransmitted through the second electrode 6617, a laminated layer of ametal thin film with a thin thickness and a transparent conductive film(an alloy of indium oxide and tin oxide (ITO), an alloy of indium oxideand zinc oxide (In₂O₃—ZnO), zinc oxide (ZnO), or the like) is preferablyused as the second electrode (cathode) 6617.

By attaching the sealing substrate 6604 to the substrate 6610 with thesealant 6605, a structure is obtained in which a light emitting element6618 is provided in the space 6607 surrounded by the substrate 6610, thesealing substrate 6604, and the sealant 6605. Note that there is also acase where the space 6607 is filled with the sealant 6605 as well as aninert gas (such as nitrogen or argon).

Note that an epoxy-based resin is preferably used as the sealant 6605.The material preferably allows as little moisture and oxygen as possibleto penetrate. As the sealing substrate 6604, a plastic substrate formedof FRP (Fiberglass-Reinforced Plastics), PVF (polyvinyl fluoride),Myler, polyester, acrylic, or the like can be used besides a glasssubstrate or a quartz substrate.

The display panel can be obtained as described above.

Furthermore, an example of an EL element applicable to the lightemitting element 6618 is shown in FIGS. 72A and 72B.

The EL element has an element structure in which an anode 7202, a holeinjecting layer 7203 formed of a hole injecting material, a holetransporting layer 7204 formed of a hole transporting material, a lightemitting layer 7205, an electron transporting layer 7206 formed of anelectron transporting material, an electron injecting layer 7207 formedof an electron injecting material, and a cathode 7208 are laminated overa substrate 7201. Here, the light emitting layer 7205 may be formed ofonly one kind of a light emitting material; however, it may be formed oftwo or more kinds of materials. In addition, an element structure of theinvention is not limited to this structure.

In addition to the laminated structure of respective functional layersshown in FIG. 72A, there is a wide range of variation in elementstructure, such as an element using a high molecular compound or ahigh-efficiency element in which a light emitting layer is formed usinga triplet light emitting material that emits light from a tripletexcited state. In addition, the element structure of the invention isalso applicable to a white display element realized by controlling acarrier recombination region with a hole blocking layer to divide alight emitting region into two regions, or the like.

In a manufacturing method of the element of the invention shown in FIG.72A, a hole injecting material, a hole transporting material, and alight emitting material are evaporated in this order over the substrate7201 provided with the anode 7202. Then, an electron transportingmaterial and an electron injecting material are evaporated, and thecathode 7208 is lastly formed by evaporation.

Suitable materials for the hole injecting material, the holetransporting material, the electron transporting material, the electroninjecting material, and the light emitting material are listed below.

As the hole injecting material, a porphyrin compound, phthalocyanine(hereinafter referred to as “H₂Pc”), copper phthalocyanine (hereinafterreferred to as “CuPc”), or the like is effective among organiccompounds. In addition, a material which has a smaller value of anionization potential than that of the hole transporting material to beused and has a hole transporting function can also be used as the holeinjecting material. There is also a chemically-doped conductive highmolecular compound, which includes polyethylenedioxythiophene(hereinafter referred to as “PEDOT”) doped with polystyrene sulfonate(hereinafter referred to as “PSS”), polyaniline, and the like. Inaddition, an insulating high molecular compound is also effective inplanarization of the anode, and polyimide (hereinafter referred to as“PI”) is often used. Further, an inorganic compound is also used, whichincludes an ultrathin film of aluminum oxide (hereinafter referred to as“alumina”) as well as a thin film of metal such as gold or platinum.

A material that is most widely used as the hole transporting material isan aromatic amine-based compound (in other words, a compound having abond of benzene ring-nitrogen). A widely-used material includes4,4′-bis(diphenylamino)-biphenyl (hereinafter referred to as “TAD”), aderivative thereof such as4,4′-bis[N-(3-methylphenyl)-N-phenyl-amino]-biphenyl (hereinafterreferred to as “TPD”) or4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereinafter referredto as “α-NPD”), and besides, a star burst aromatic amine compound suchas 4,4′,4″-tris(N,N-diphenyl-amino)-triphenylamine (hereinafter referredto as “TDATA”) or4,4′,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenylamine(hereinafter referred to as “MTDATA”).

As the electron transporting material, a metal complex is often used,which includes a metal complex having a quinoline skeleton or abenzoquinoline skeleton such as Alq₃, BAlq,tris(4-methyl-8-quinolinolato)aluminum (hereinafter referred to as“Almq”), or bis(10-hydroxybenzo[h]-quinolinato)beryllium (hereinafterreferred to as “Bebq”), and besides, a metal complex having anoxazole-based or a thiazole-based ligand such asbis[2-(2-hydroxyphenyl)-benzoxazolato]zinc (hereinafter referred to as“Zn(BOX)₂”) or bis[2-(2-hydroxyphenyl)-benzothiazolato]zinc (hereinafterreferred to as “Zn(BTZ)₂”). Further, other than the metal complex, anoxadiazole derivative such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (hereinafterreferred to as “PBD”) or OXD-7, a triazole derivative such as TAZ or3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(hereinafter referred to as “p-EtTAZ”), and a phenanthroline derivativesuch as bathophenanthroline (hereinafter referred to as “BPhen”) or BCPhave an electron transporting property.

As the electron injecting material, the above-described electrontransporting materials can be used. In addition, an ultrathin film of aninsulator such as metal halide including calcium fluoride, lithiumfluoride, cesium fluoride, and the like, or alkali metal oxide includinglithium oxide, and the like is often used. Further, an alkali metalcomplex such as lithium acetyl acetonate (hereinafter referred to as“Li(acac)”) or 8-quinolinolato-lithium (hereinafter referred to as“Liq”) is also effective.

As the light emitting material, other than the above-described metalcomplex such as Alq₃, Almq, BeBq, BAlq, Zn(BOX)₂, or Zn(BTZ)₂, variousfluorescent pigments are effective. The fluorescent pigments include4,4′-bis(2,2-diphenyl-vinyl)-biphenyl which is blue,4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran whichis red-orange, and the like. In addition, a triplet light emittingmaterial is also possible, which is mainly a complex with platinum oriridium as central metal. As the triplet light emitting material,tris(2-phenylpyridine)iridium,bis(2-(4′-tryl)pyridinato-N,C^(2′))acetylacetonato iridium (hereinafterreferred to as “acacIr(tpy)₂”),2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin-platinum, and the likeare known.

By combining the above-described materials that have respectivefunctions, a highly reliable display element can be manufactured.

In addition, a display element having layers laminated in reverse orderof that in FIG. 72A can also be used as shown in FIG. 72B. In otherwords, in an element structure, the cathode 7208, the electron injectinglayer 7207 formed of an electron injecting material, the electrontransporting layer 7206 formed of an electron transporting material, thelight emitting layer 7205, the hole transporting layer 7204 formed of ahole transporting material, the hole injecting layer 7203 formed of ahole injecting material, and the anode 7202 are sequentially laminatedover the substrate 7201.

In addition, in order to extract light emission of a light emittingelement, at least one of the anode and the cathode may be transparent.Then, a TFT and a display element are formed over a substrate. There arelight emitting elements having a top emission structure in which lightemission is extracted through the surface opposite to the substrate,having a bottom emission structure in which light emission is extractedthrough the surface on the substrate side, and having a dual emissionstructure in which light emission is extracted through the surfaceopposite to the substrate and the surface on the substrate side. Thepixel configuration of the invention can be applied to a display elementhaving any of the emission structures.

A light emitting element having the top emission structure is describedwith reference to FIG. 73A.

Over a substrate 7300, a TFT 7301 is formed, and a first electrode 7302is formed in contact with a source electrode of the TFT 7301. A layer7303 containing an organic compound and a second electrode 7304 areformed thereover.

Note that the first electrode 7302 is an anode of the light emittingelement, and the second electrode 7304 is a cathode of the lightemitting element. In other words, the light emitting element is formedin a region where the layer 7303 containing an organic compound issandwiched between the first electrode 7302 and the second electrode7304.

Here, the first electrode 7302 which functions as an anode is preferablyformed using a material having a high work function. For example, asingle-layer film such as a titanium nitride film, a chromium film, atungsten film, a Zn film, or a Pt film, a laminated layer of a titaniumnitride film and a film containing aluminum as its main component, or athree-layer structure of a titanium nitride film, a film containingaluminum as its main component, and a titanium nitride film, or the likecan be used. Note that when the first electrode 7302 has a laminatedstructure, it can have low resistance as a wire, form a good ohmiccontact, and function as an anode. By using a light-reflective metalfilm, an anode which does not transmit light can be formed.

The second electrode 7304 which functions as a cathode is preferablyformed using a laminated layer of a metal thin film formed of a materialhaving a low work function (Al, Ag, Li, Ca, or an alloy thereof such asMgAg, MgIn, AlLi, CaF₂, or Ca₃N₂) and a transparent conductive film(indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), orthe like). By using the thin metal film and the transparent conductivefilm as described above, a cathode which can transmit light can beformed.

Thus, light of the light emitting element can be extracted from a topsurface as indicated by an arrow in FIG. 73A. In other words, in thecase of applying the light emitting element to the display panel shownin FIGS. 71A and 71B, light is emitted toward the substrate 7145 side.Therefore, when a light emitting element having a top emission structureis used for the display device, a substrate which transmits light isused as the substrate 7145.

In addition, in the case of providing an optical film, the optical filmmay be provided over the substrate 7145.

Note that the first electrode 7302 can be formed using a metal filmformed of a material having a low work function such as MgAg, MgIn, orAlLi to function as a cathode in the case of the pixel structuredescribed in Embodiment Mode 7. In this case, the second electrode 7304can be formed using a transparent conductive film such as an indium tinoxide (ITO) film or an indium zinc oxide (IZO) film. Consequently, withthis structure, the transmittance of the top emission can be improved.

A light emitting element having the bottom emission structure isdescribed with reference to FIG. 73B. Description is made using the samereference numerals as those in FIG. 73A since a structure except for itsemission structure is identical.

Here, the first electrode 7302 which functions as an anode is preferablyformed using a material having a high work function. For example, atransparent conductive film such as an indium tin oxide (ITO) film or anindium zinc oxide (IZO) film can be used. By using a transparentconductive film, an anode which can transmit light can be formed.

The second electrode 7304 which functions as a cathode can be formedusing a metal film formed of a material having a low work function (Al,Ag, Li, Ca, or an alloy thereof such as MgAg, MgIn, AlLi, CaF₂, orCa₃N₂). By using a light-reflective metal film as described above, acathode which does not transmit light can be formed.

Thus, light of the light emitting element can be extracted from a bottomsurface as indicated by an arrow in FIG. 73B. In other words, in thecase of applying the light emitting element to the display panel shownin FIGS. 71A and 71B, light is emitted toward the substrate 7100 side.Therefore, when the light emitting element having a bottom emissionstructure is used for the display device, a substrate which transmitslight is used as the substrate 7100.

In addition, in the case of providing an optical film, the optical filmmay be provided over the substrate 7100.

A light emitting element having the dual emission structure is explainedwith reference to FIG. 73C. Description is made using the same referencenumerals as those in FIG. 73A since a structure except for its emissionstructure is identical.

Here, the first electrode 7302 which functions as an anode is preferablyformed using a material having a high work function. For example, atransparent conductive film such as an indium tin oxide (ITO) film or anindium zinc oxide (IZO) film can be used. By using a transparentconductive film, an anode which can transmit light can be formed.

The second electrode 7304 which functions as a cathode is preferablyformed using a laminated layer of a metal thin film formed of a materialhaving a low work function (Al, Ag, Li, Ca, or an alloy thereof such asMgAg, MgIn, AlLi, CaF₂, or Ca₃N₂) and a transparent conductive film(indium tin oxide (ITO), an alloy of indium oxide and zinc oxide(In₂O₃—ZnO), zinc oxide (ZnO), or the like). By using the thin metalfilm and the transparent conductive film as described above, a cathodewhich can transmit light can be formed.

Thus, light of the light emitting element can be extracted from bothsurfaces as indicated by arrows in FIG. 73C. In other words, in the caseof applying the light emitting element to the display panel shown inFIGS. 71A and 71B, light is emitted toward the substrate 7100 side andthe substrate 7145 side. Therefore, when the light emitting elementhaving a dual emission structure is used for the display device,substrates which transmit light are used as both the substrate 7100 andthe substrate 7145.

In addition, in the case of providing an optical film, the optical filmmay be provided over both the substrate 7100 and the substrate 7145.

In addition, the invention can be applied to a display device whichachieves full-color display by using a white light emitting element anda color filter.

As shown in FIG. 74, a TFT 7401 is formed over a substrate 7400, and afirst electrode 7403 is formed in contact with a source electrode of theTFT 7401. A layer 7404 containing an organic compound and a secondelectrode 7405 are formed thereover.

Note that the first electrode 7403 is an anode of the light emittingelement, and the second electrode 7405 is a cathode of the lightemitting element. In other words, the light emitting element is formedin a region where the layer 7404 containing an organic compound issandwiched between the first electrode 7403 and the second electrode7405. White light is emitted with the structure shown in FIG. 74. A redcolor filter 7406R, a green color filter 7406G, and a blue color filter7406B are provided above the light emitting elements respectively toachieve full-color display. In addition, a black matrix (also referredto as a “BM”) 7407 which separates these color filters is provided.

The above-described structures of the light emitting element can be usedin combination and can be appropriately applied to the display panel ofthe invention. Note that the light emitting elements described above aremerely examples, and a display device having another structure can alsobe applied.

Embodiment 3

A display panel of the present invention can be applied to variouselectronic devices. Specifically, it can be applied to a display portionof an electronic device. Examples of such an electronic device are asfollows: a camera such as a video camera or a digital camera, a goggletype display (a head-mounted display), a navigation system, a soundreproducing device (such as a car audio or an audio component), acomputer, a game machine, a portable information terminal (such as amobile computer, a mobile phone, a portable game machine, or anelectronic book), an image reproducing device provided with a recordingmedium reading portion (specifically, a device which can reproduce arecording medium such as a digital versatile disc (DVD) and includes alight emitting device capable of displaying images thereof), and thelike.

FIG. 65A shows a light emitting device, which includes a chassis 65001,a support 65002, a display portion 65003, a speaker portion 65004, avideo input terminal 65005, and the like. The display device of thepresent invention can be used for the display portion 65003. Note thatthe light emitting device includes in its category all light emittingdevices used for displaying information, for example, for a personalcomputer, for TV broadcast reception, or for advertisement display. Thelight emitting device using the display panel of the present inventionfor the display portion 65003 can prevent defective display.

FIG. 65B shows a camera, which includes a main body 65101, a displayportion 65102, an image receiving portion 65013, an operation key 65104,an external connection port 65105, a shutter 65106, and the like.

The camera using the display panel of the present invention for thedisplay portion 65102 can prevent defective display.

FIG. 65C shows a computer, which includes a main body 65201, a chassis65202, a display portion 65203, a keyboard 65204, an external connectionport 65205, a pointing mouse 65206, and the like. The computer using thedisplay panel of the present invention for the display portion 65203 canprevent defective display.

FIG. 65D shows a mobile computer, which includes a main body 65301, adisplay portion 65302, a switch 65303, an operation key 65304, aninfrared port 65305, and the like. The mobile computer using the displaypanel of the present invention for the display portion 65302 can preventdefective display.

FIG. 65E shows a portable image reproducing device provided with arecording medium reading portion (specifically, a DVD reproducingdevice), which includes a main body 65401, a chassis 65402, a displayportion A 65403, a display portion B 65404, a recording medium (DVD orthe like) reading portion 65405, an operation key 65406, a speakerportion 65407, and the like. The display portion A 65403 mainly displaysimage information, and the display portion B 65404 mainly displayscharacter information. The image reproducing device using the displaypanel of the present invention for the display portion A 65403 and thedisplay portion B 65404 can prevent defective display.

FIG. 65F shows a goggle type display, which includes a main body 65501,a display portion 65502, an arm portion 65503, and the like. The goggletype display using the display panel of the present invention for thedisplay portion 65502 can prevent defective display.

FIG. 65G shows a video camera, which includes a main body 652001, adisplay portion 652002, a chassis 652003, an external connection port652004, a remote control receiving portion 652005, an image receivingportion 652006, a battery 652007, an audio input portion 652008, anoperation key 652009, and the like. The video camera using the displaypanel of the present invention for the display portion 652002 canprevent defective display.

FIG. 65H shows a mobile phone, which includes a main body 65701, achassis 65702, a display portion 65703, an audio input portion 65704, anaudio output portion 65705, an operation key 65706, an externalconnection port 65707, an antenna 65708, and the like. The mobile phoneusing the display panel of the present invention for the display portion65703 can prevent defective display.

As described above, the display panel of the present invention can beapplied to all electronic devices.

Embodiment 4

In this embodiment, an example of a structure of a mobile phone whichhas the display panel of the invention in a display portion is explainedwith reference to FIG. 64.

A display panel 6410 is incorporated in a housing 6400 so as to bedetachable. The shape and size of the housing 6400 can be appropriatelychanged in accordance with the size of the display panel 6410. Thehousing 6400 to which the display panel 6410 is fixed is fitted in aprinted circuit board 6401 to be assembled as a module.

The display panel 6410 is connected to the printed circuit board 6401via an FPC 6411. Over the printed circuit board 6401, a speaker 6402, amicrophone 6403, a transmitting and receiving circuit 6404, and a signalprocessing circuit 6405 including a CPU, a controller, and the like areformed. Such a module, an input means 6406, and a battery 6407 arecombined and stored in a chassis 6409. A pixel portion of the displaypanel 6410 is arranged so as to be seen from a window formed in thechassis 6409.

Note that the structure described in this embodiment is an example of amobile phone, and the display device of the invention can be applied notonly to the mobile phone having the above-described structure but alsoto mobile phones having various kinds of structures.

Embodiment 5

FIG. 62 shows an EL module in which a display panel 6201 and a circuitboard 6202 are combined. The display panel 6201 includes a pixel portion6203, a scan line driver circuit 6204, and a signal line driver circuit6205. Over the circuit board 6202, for example, a control circuit 6206,a signal dividing circuit 6207, and the like are formed. The displaypanel 6201 and the circuit board 6202 are connected to each other by aconnection wiring 6208. As the connection wiring, an FPC or the like canbe used.

An EL television receiver can be completed with this EL module. FIG. 63is a block diagram showing main constitution of the EL televisionreceiver. A tuner 6301 receives a video signal and an audio signal. Thevideo signal is processed by a video signal amplifier circuit 6302, avideo signal processing circuit 6303 for converting a signal output fromthe video signal amplifier circuit 6302 into a color signalcorresponding to each color of red, green and blue, and a controlcircuit 6206 for converting the video signal into the inputspecification of a driver circuit. The control circuit 6206 outputs asignal to each of the scan line side and the signal line side. In thecase of digital drive, constitution in which the signal dividing circuit6207 is provided on the signal line side to supply an input digitalsignal divided into m pieces may be adopted.

An audio signal among signals received by the tuner 6301 is transmittedto an audio signal amplifier circuit 6304, an output of which issupplied to a speaker 6306 through an audio signal processing circuit6305. A control circuit 6307 receives control information of a receivingstation (reception frequency) or sound volume from an input portion 6308and transmits signals to the tuner 6301 and the audio signal processingcircuit 6305.

By incorporating the EL module shown in FIG. 62 into a chassis 65001, aTV receiver can be completed as shown in FIG. 65A. A display portion65003 is formed with the EL module. In addition, a speaker 65004, avideo input terminal 65005, and the like are provided appropriately.

Naturally, the invention is not limited to the TV receiver, and can beapplied to various use applications particularly as a large-sizeddisplay medium such as an information display board at a train station,an airport, or the like, or an advertisement display board on thestreet, as well as a monitor of a personal computer.

Embodiment 6

In this embodiment, a favorable structure of a display panel including acomposite connection pad in a connection terminal portion is explained.

First, a structure of connection pads (a reference connection pad and acomposite connection pad) in a connection terminal portion of a displaypanel is explained with reference to FIG. 67.

A continuous conductive film is formed over a substrate 6701, theconductive film within a region of the connection terminal portionfunctions as a connection pad, and the conductive film within a regionof a wiring portion functions as a wire. In FIG. 67, a referenceconnection pad 6703 and a wire 6706 are formed with one continuousconductive film. In addition, a composite connection pad 6704, a wire6707, and a wire 6708 are formed with one continuous conductive film.Further, a composite connection pad 6705, a wire 6709, a wire 6710, anda wire 6711 are formed with one continuous conductive film.

In a sealing region 6702, an opposite substrate provided opposite to thesubstrate 6701 is attached with a sealant.

Note that the composite connection pad 6704 is connected to two FPC padsand the composite connection pad 6705 is connected to three FPC pads.

Here, the line width of the reference connection pad 6703 is denoted byW, the line width of the composite connection pad 6704 is denoted by W′,and the line width of the composite connection pad 6705 is denoted byW″. In addition, the distance between line-width centers of adjacentreference connection pads is denoted by L.

Here, the distance between the line-width center of the compositeconnection pad 6704 and the line-width center of the referenceconnection pad is 1.5 times of L, and the distance between theline-width center of the composite connection pad 6705 and theline-width center of the reference connection pad is twice of L.Therefore, an FPC terminal array does not need to be changed, and an FPCcan be used without any change in the specification.

Note that the line-width W′ of the composite connection pad 6704 ispreferably larger than the distance L between the line-width centers ofadjacent reference connection pads. In addition, the line-width W″ ofthe composite connection pad 6705 is preferably more than twice as largeas L. This can decrease the contact resistance between the connectionpad and the FPC pad.

Subsequently, the role of a plurality of wires electrically connected toa composite connection pad in a display panel is explained.

In a display panel including, for example, two scan line drivercircuits, a wire 6707 in FIG. 67 is electrically connected to one of thescan line driver circuits, and a wire 6708 in FIG. 67 is electricallyconnected to the other scan line driver circuit. In other words,respective wires for supplying common signals or common power to twoscan line driver circuits are electrically connected to one connectionpad. Thus, malfunctions of two scan line driver circuits can beprevented.

As another structure, in a display panel including a pixel portion and aperipheral driver circuit for driving a pixel, in which the peripheraldriver circuit includes a shift register and a buffer circuit, the wire6707 in FIG. 67 is electrically connected to the shift register and thewire 6708 in FIG. 67 is electrically connected to the buffer circuit. Inother words, respective wires for supplying common power to the shiftregister and the buffer circuit are electrically connected to oneconnection pad. In other words, as shown in FIG. 68B, a wire 6804 is awire for supplying power of a shift register 6801 and is electricallyconnected to the wire 6707 in FIG. 67. In addition, a wire 6805 is awire for supplying power of a buffer circuit 6802 and is electricallyconnected to the wire 6708 in FIG. 67. Here, if power is supplied to theshift register 6801 and the buffer circuit 6802 through a wire 6803 asshown in FIG. 68A, a power supply potential of the wire 6803 isdecreased when the buffer circuit 6802 is to output a large current.Consequently, the shift register 6801 does not operate normally. Thus,by employing the structure shown in FIG. 68B, a malfunction of the shiftregister 6801 can be prevented.

As another structure, in a liquid crystal display panel including aliquid crystal element in a pixel, the wire 6707 and the wire 6708 inFIG. 67 are electrically connected to an opposite electrode. In otherwords, respective wires for supplying a power supply potential servingas a power source to the opposite electrode are electrically connectedto one connection pad. Particularly in the liquid crystal display panel,a potential of the opposite electrode is changed in order to achievelonger life of the liquid crystal element by reversing the polarity of avoltage applied to the liquid crystal element. By decreasing theresistance of a power supply line as in this structure, powerconsumption can be reduced.

As another structure, in an EL display panel having an EL element in apixel, the wire 6707 and the wire 6708 in FIG. 67 are electricallyconnected to a power supply line or an opposite electrode. In otherwords, respective wires for supplying a power supply potential servingas a power source to the opposite electrode or the power supply line areelectrically connected to one connection pad. Particularly in the ELdisplay panel, a large amount of current flows to the EL element.Therefore, when the power supply line has high resistance, a desiredpower supply potential cannot be obtained due to a voltage drop. Bydecreasing the resistance of the power supply line as in this structure,defective display can be prevented.

As another structure, in a display panel including a light emittingelement in a pixel, the wire 6707 in FIG. 67 is electrically connectedto an opposite electrode and the wire 6708 in FIG. 67 is electricallyconnected to a wire (referred to as an auxiliary wire) provided incontact with the opposite electrode. In other words, respective wiresfor supplying common power to the opposite electrode and the auxiliarywire are electrically connected to one connection pad. Note that across-sectional structure of the display panel in this case is explainedwith reference to FIG. 75.

A base film 7502 is formed over a substrate 7501. An insulatingsubstrate, a metal substrate, a semiconductor substrate, or the likesuch as a glass substrate, a quartz substrate, a plastic substrate, or aceramics substrate can be used as the substrate 7501. The base film 7502can be formed by a CVD method or a sputtering method. For example, asilicon oxide film, a silicon nitride film, a silicon oxynitride film,or the like which is formed by a CVD method using SiH₄, N₂O, NH₃, or thelike as a source material can be employed. Alternatively, a laminatethereof may be used. Note that the base film 7502 is provided to preventan impurity from diffusing into a semiconductor layer from the substrate7501, and the base film 7502 is not necessarily provided in the case ofusing a glass substrate or a quartz substrate as the substrate 7501.

An island-shaped semiconductor layer is formed over the base film 7502.In the semiconductor layer, a channel formation region 7505, an impurityregion 7506 serving as a source region or a drain region, and alow-concentration impurity region (LDD region) 7507 of a transistor 7503and a channel formation region 7508, an impurity region 7509 serving asa source region or a drain region, and a low-concentration impurityregion (LDD region) 7510 of a transistor 7504 are formed. Then, a gateelectrode 7512 and a gate electrode 7513 are formed over the channelformation region 7505 and the channel formation region 7508 with a gateinsulating film 7511 therebetween. The gate insulating film 7511 can beformed using a silicon oxide film, a silicon nitride film, a siliconoxynitride film, or the like by a CVD method or a sputtering method. Inaddition, the gate electrode 7512 and the gate electrode 7513 can beformed using an aluminum (Al) film, a copper (Cu) film, a thin filmcontaining aluminum or copper as its main component, a chromium (Cr)film, a tantalum (Ta) film, a tantalum nitride (TaN) film, a titanium(Ti) film, a tungsten (W) film, a molybdenum (Mo) film, or the like.

A sidewall 7514 is formed on the side of the gate electrode 7512, and asidewall 7515 is formed on the side of the gate electrode 7513. Thesidewall 7514 and the sidewall 7515 can be formed by forming a siliconcompound such as a silicon oxide film, a silicon nitride film, or asilicon oxynitride film to cover the gate electrode 7512 and the gateelectrode 7513, and then etching back it.

Note that the low-concentration impurity region 7507 and thelow-concentration impurity region 7510 are located below the sidewall7514 and the sidewall 7515, respectively. In other words, thelow-concentration impurity region 7507 and the low-concentrationimpurity region 7510 are formed in a self-aligned manner. Note that thesidewall 7514 and the sidewall 7515 are provided to form thelow-concentration impurity region 7507 and the low-concentrationimpurity region 7510 in a self-aligned manner, and the sidewalls are notnecessarily provided.

A first interlayer insulating film is formed over the gate electrode7512, the gate electrode 7513, the sidewall 7514, the sidewall 7515, andthe gate insulating film 7511. The first interlayer insulating filmincludes an inorganic insulating film 7516 as a lower layer and a resinfilm 7517 as an upper layer. As the inorganic insulating film 7516, asilicon nitride film, a silicon oxide film, a silicon oxynitride film,or a laminated film thereof can be used. As the resin film 7517,polyimide, polyamide, acrylic, polyimide amide, epoxy, or the like canbe used.

A wire 7518, a wire 7519, and a wire 7520 are formed over the firstinterlayer insulating film, and the wire 7518 is electrically connectedto the impurity region 7506 through a contact hole; the wire 7519 iselectrically connected to the impurity region 7506 and the impurityregion 7509 through contact holes; and the wire 7520 is electricallyconnected to the impurity region 7509 through a contact hole. The wire7518, the wire 7519, and the wire 7520 can be formed using a titanium(Ti) film, an aluminum (Al) film, a copper (Cu) film, an aluminum filmcontaining Ti, or the like. Note that in the case where a wire such as asignal line is provided in the same layer as the wire 7518, the wire7519, and the wire 7520, copper which has low resistance is preferablyused.

A second interlayer insulating film 7521 is formed over the wire 7518,the wire 7519, the wire 7520, and the first interlayer insulating film.The second interlayer insulating film 7521 can be formed using aninorganic insulating film, a resin film, or a laminated layer thereof.As the inorganic insulating film, a silicon nitride film, a siliconoxide film, a silicon oxynitride film, or a laminated layer thereof canbe used. As the resin film, polyimide, polyamide, acrylic, polyimideamide, epoxy, or the like can be used.

A pixel electrode 7522 and a wire 7523 are formed over the secondinterlayer insulating film 7521. The pixel electrode 7522 and the wire7523 are formed from the same material. In other words, they are formedin the same layer simultaneously. A material having a high work functionis preferably used for the pixel electrode 7522 and the wire 7523. Forexample, a single-layer film such as a titanium nitride (TiN) film, achromium (Cr) film, a tungsten (W) film, a zinc (Zn) film, or a platinum(Pt) film; a laminated layer of a titanium nitride film and a filmcontaining aluminum as its main component; a three-layer structure of atitanium nitride film, a film containing aluminum as its main component,and a titanium nitride film; or the like can be used. When the pixelelectrode 7522 and the wire 7523 have laminated structures, they canhave low resistance as a wire and form a favorable ohmic contact.Further, the pixel electrode and the wire can function as an anode. Byusing a light-reflecting metal film, an anode which does not transmitlight can be formed.

An insulator 7524 is formed to cover end portions of the pixel electrode7522 and the wire 7523. For example, a positive type photosensitiveacrylic resin film can be used as the insulator 7524.

A layer 7525 containing an organic compound is formed over the pixelelectrode 7522, and part of the layer 7525 containing an organiccompound overlaps the insulator 7524. Note that the layer 7525containing an organic compound is not formed over the wire 7523.

An opposite electrode 7526 is formed over the layer 7525 containing anorganic compound, the insulator 7524, and the wire 7523. For theopposite electrode 7526, a material having a low work function ispreferably used. For example, a metal thin film of aluminum (Al), silver(Ag), lithium (Li), calcium (Ca), an alloy thereof such as MgAg, MgIn,AlLi, CaF₂, or Ca₃N₂, or the like can be used. By using a thin metalfilm in this manner, a cathode which can transmit light can be formed.

A light emitting element 7527 is formed in a region where the layer 7525containing an organic compound is sandwiched between the oppositeelectrode 7526 and the pixel electrode 7522.

In a region where the layer 7525 containing an organic compound isseparated by the insulator 7524, a junction portion 7528 is formed, inwhich the opposite electrode 7526 and the wire 7523 are in contact witheach other. Therefore, the wire 7523 functions as an auxiliary electrodeof the opposite electrode 7526, and the resistance of the oppositeelectrode 7526 can be decreased. Consequently, the thickness of theopposite electrode 7526 can be thinned and the transmission thereof canbe increased. Accordingly, in a display panel having a structure inwhich light obtained from the light emitting element 7527 is extractedfrom the top surface, higher luminance can be obtained.

Note that the opposite electrode 7526 may be formed using a laminatedlayer of a thin metal film and a transparent conductive film (indium tinoxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), or the like) inorder to further decrease the resistance thereof. By using the thinmetal film and the transparent conductive film as described above, acathode which can transmit light can also be formed.

Note that the impurity region 7506 and the impurity region 7509 aredoped with an n-type impurity. Therefore, the transistor 7503 and thetransistor 7504 are n-channel transistors.

Note that the display panel explained with FIG. 75, in which theopposite electrode 7526 can be thinned, exhibits a highlight-transmitting property with respect to light to be emitted from thetop surface. Accordingly, the luminance of the top emission can beincreased. In addition, by connecting the wire 7523 to the oppositeelectrode 7526, the resistance of the opposite electrode 7526 can bedecreased. Accordingly, power consumption can be reduced. Note that thewire 7523 is an auxiliary wire.

Next, a structure of a display panel is explained with reference toschematic top views thereof shown in FIGS. 76A and 76B. A signal linedriver circuit 7601, a scan line driver circuit 7602, and a pixelportion 7603 are formed over a substrate 7600. Note that the substrate7600 is connected to an FPC (Flexible Printed Circuit) 7604, and signalssuch as a video signal, a clock signal, and a start signal to beinputted to the signal line driver circuit 7601 and the scan line drivercircuit 7602 are supplied through the FPC 7604. On the junction of theFPC 7604 and the substrate 7600, an IC chip (a semiconductor chipprovided with a memory circuit, a buffer circuit, or the like) 7605 ismounted by COG (Chip On Glass) or the like. Although only the FPC 7604is illustrated here, a printed wiring board (PWB) may be attached to theFPC 7604. The display device in this specification includes not only amain body of a display panel but also a display panel provided with anFPC or a PWB, and besides, a display panel mounted with an IC chip orthe like.

Pixels are arranged in matrix in the pixel portion 7603 of the displaypanel shown in FIG. 76A to form a pixel column for each color element. Alayer 7607 containing an organic compound is provided over pixels of onecolumn for each color. In addition, in the pixel portion, a junctionportion of a wire formed of the same material as a pixel electrode andan opposite electrode is formed in a region 7606 other than the regionwhere the layer 7607 containing an organic compound is provided. Inother words, the junction portion 7528 shown in the cross-sectional viewof FIG. 75 is formed in the region 7606 in FIG. 76B. A schematic topview of the pixel portion is shown in FIG. 77. In FIG. 77, a wire 7702is formed of the same material as a pixel electrode 7701. In addition,the pixel electrode 7701 corresponds to the pixel electrode 7522 in FIG.75 and the wire 7702 corresponds to the wire 7523 in FIG. 75. A layercontaining an organic compound is formed over the pixel electrode 7701of one column, and a light emitting element is formed in a region wherethe layer containing an organic compound is sandwiched between the pixelelectrode 7701 and an opposite electrode. Since the wire 7702 is incontact with the opposite electrode in the junction portion, theresistance of the opposite electrode can be decreased. In other words,the wire 7702 functions as an auxiliary electrode of the oppositeelectrode. Note that by employing the structure of the pixel portion asshown in FIG. 77, a display panel having a high aperture ratio, in whichthe resistance of the opposite electrode is decreased, can be provided.

Pixels are arranged in matrix in the pixel portion 7603 of the displaypanel shown in FIG. 76B to form a pixel column for each color element. Alayer 7617 containing an organic compound is provided for pixels of onecolumn for each color. In addition, in the pixel portion, a junctionportion of a wire formed of the same material as a pixel electrode andan opposite electrode is formed in a region 7616 other than the regionwhere the layer 7617 containing an organic compound is provided. Inother words, the junction portion 7528 shown in the cross-sectional viewof FIG. 75 is formed in the region 7616 in FIG. 76B. A schematic topview of the pixel portion is shown in FIG. 78. In FIG. 78, a wire 7802is formed of the same material as a pixel electrode 7801. In addition,the pixel electrode 7801 corresponds to the pixel electrode 7522 in FIG.75 and the wire 7802 corresponds to the wire 7523 in FIG. 75. A layercontaining an organic compound is formed over each pixel electrode 7801,and a light emitting element is formed in a region where the layercontaining an organic compound is sandwiched between the pixel electrode7801 and an opposite electrode. Since the wire 7802 is in contact withthe opposite electrode in the junction portion, the resistance of theopposite electrode can be decreased. In other words, the wire 7802functions as an auxiliary electrode of the opposite electrode. Note thatby employing the structure of the pixel portion as shown in FIG. 78, adisplay panel in which the resistance of the opposite electrode isdecreased can be provided.

The display panel described in this embodiment, in which the oppositeelectrode has a high light-transmitting property, has a high pixelaperture ratio. Therefore, necessary light intensity can be obtainedeven when luminance is decreased. Accordingly, the reliability of thelight emitting element can be improved. In addition, the resistance ofthe opposite electrode can be decreased; thus, power consumption canalso be reduced.

Further, the display panel is explained using a schematic diagram.

A display panel in FIG. 69 includes, over a substrate 6901, a signalline driver circuit 6903, a first scan line driver circuit 6904, asecond scan line driver circuit 6905, a pixel portion 6906, and aconnection terminal portion 6907. The substrate 6901 and an oppositesubstrate are attached to each other in a sealing region 6902, and thesignal line driver circuit 6903, the first scan line driver circuit6904, and the second scan line driver circuit 6905 are sealed.

The connection terminal portion 6907 includes a plurality of connectionpads. Among the plurality of connection pads, a reference connection pad6908 is electrically connected to a wire 6910. A composite connectionpad 6909 is electrically connected to a wire 6911 and a wire 6912. Thewire 6911 and the wire 6912 are electrically connected to the signalline driver circuit 6903. For example, as shown in FIG. 68B, one of thewire 6911 and the wire 6912 is electrically connected to a wire forsupplying power of a shift register in the signal line driver circuit6903, and the other is electrically connected to a wire for supplyingpower of a buffer circuit in the signal line driver circuit 6903.

A display panel in FIG. 70 includes, over a substrate 7001, a signalline driver circuit 7003, a first scan line driver circuit 7004, asecond scan line driver circuit 7005, a pixel portion 7006, and aconnection terminal portion 7007. The substrate 7001 and an oppositesubstrate are attached to each other in a sealing region 7002, and thesignal line driver circuit 7003, the first scan line driver circuit7004, and the second scan line driver circuit 7005 are sealed.

The connection terminal portion 7007 includes a plurality of connectionpads. Among the plurality of connection pads, a reference connection pad7008 is electrically connected to a wire 7010. A composite connectionpad 7009 is electrically connected to a wire 7011 and a wire 7012. Thewire 7011 is electrically connected to the first scan line drivercircuit 7004, and the wire 7012 is electrically connected to the secondscan line driver circuit 7005.

Embodiment 7

In this embodiment, another structure applicable to the light emittingelement of the invention is explained with reference to FIGS. 79A to 79Cand FIGS. 80A to 80C.

Light emitting elements utilizing electroluminescence are classifiedaccording to whether a light emitting element is an organic compound oran inorganic compound. In general, the former is referred to as anorganic EL element, and the latter is referred to as an inorganic ELelement.

The inorganic EL elements are classified according to their elementstructures into a dispersed inorganic EL element and a thin-filminorganic EL element. They are different in that the former includes anelectroluminescent layer in which particles of a light emitting materialare dispersed in a binder and the latter includes an electroluminescentlayer formed from a thin film of a light emitting material; however,they are common in that electrons accelerated by a high electric fieldare required. Note that a mechanism for obtainable light emissionincludes a donor-acceptor recombination light emission which utilizes adonor level and an acceptor level and a localized light emission whichutilizes inner-shell electron transition of metal ions. In general, itis often the case that the dispersed inorganic EL element performs thedonor-acceptor recombination light emission and the thin-film inorganicEL element performs the localized light emission.

A light emitting material which can be used in the present inventionincludes a base material and an impurity element serving as a lightemitting center. Light emission of various colors can be obtained bychanging impurity elements to be contained. As a method for producing alight emitting material, various methods such as a solid phase methodand a liquid phase method (co-precipitation method) can be used. Inaddition, a liquid phase method such as a spray pyrolysis method, adouble decomposition method, a method by precursor pyrolysis, a reversemicelle method, a combined method of these methods and high-temperaturebaking, or a freeze-drying method can be used.

The solid phase method is a method in which a base material and animpurity element or a compound containing an impurity element areweighed, mixed in a mortar, and reacted by heating and baking in anelectric furnace to make the impurity element contained in the basematerial. The baking temperature is preferably in the range of 700° C.to 1500° C. This is because solid phase reaction does not proceed whenthe temperature is too low and the base material is decomposed when thetemperature is too high. Note that the baking may be performed in powderform, but the baking is preferably performed in pellet form. The methodrequires baking at a relatively high temperature; however, it is asimple method. Therefore, the method has good productivity and issuitable for mass production.

The liquid phase method (co-precipitation method) is a method in which abase material or a compound containing a base material is reacted in asolution with an impurity element or a compound containing an impurityelement and the reactant is baked after being dried. Particles of thelight emitting material are uniformly distributed, a particle size issmall, and the reaction proceeds even at a low baking temperature.

As the base material used for a light emitting material, sulfide, oxide,or nitride can be used. As sulfide, zinc sulfide (ZnS), cadmium sulfide(CdS), calcium sulfide (CaS), yttrium sulfide (Y₂S₃), gallium sulfide(Ga₂S₃), strontium sulfide (SrS), barium sulfide (BaS), or the like canbe used, for example. As oxide, zinc oxide (ZnO), yttrium oxide (Y₂O₃),or the like can be used, for example. As nitride, aluminum nitride(AlN), gallium nitride (GaN), indium nitride (InN), or the like can beused, for example. Further, zinc selenide (ZnSe), zinc telluride (ZnTe),or the like can also be used. It may be ternary mixed crystal such ascalcium gallium sulfide (CaGa₂S₄), strontium gallium sulfide (SrGa₂S₄),barium gallium sulfide (BaGa₂S₄), or the like.

As the light emitting center of localized light emission, manganese(Mn), copper (Cu), samarium (Sm), terbium (Tb), erbium (Er), thulium(Tm), europium (Eu), cerium (Ce), praseodymium (Pr), or the like can beused. Note that a halogen element such as fluorine (F) or chlorine (Cl)may be added as a charge compensation.

On the other hand, as the light emitting center of donor-acceptorrecombination light emission, a light emitting material which contains afirst impurity element forming a donor level and a second impurityelement forming an acceptor level can be used. As the first impurityelement, fluorine (F), chlorine (Cl), aluminum (Al), or the like can beused, for example. As the second impurity element, copper (Cu), silver(Ag), or the like can be used, for example.

In the case of synthesizing the light emitting material ofdonor-acceptor recombination light emission by a solid phase method, abase material, a first impurity element or a compound containing a firstimpurity element, and a second impurity element or a compound containinga second impurity element are separately weighed, mixed in a mortar, andthen heated and baked in an electric furnace. As the base material, theabove-mentioned base material can be used. As the first impurity elementor the compound containing the first impurity element, fluorine (F),chlorine (Cl), aluminum sulfate (Al₂S₃), or the like can be used, forexample. As the second impurity element or the compound containing thesecond impurity element, copper (Cu), silver (Ag), copper sulfide(Cu₂S), silver sulfide (Ag₂S), or the like can be used, for example. Thebaking temperature is preferably in the range of 700° C. to 1500° C.This is because solid phase reaction does not proceed when thetemperature is too low and the base material is decomposed when thetemperature is too high. Note that the baking may be performed in powderform, but the baking is preferably performed in pellet form.

As the impurity element in the case of utilizing solid phase reaction, acompound including the first impurity element and the second impurityelement may be used. In this case, the impurity element is easilydiffused and the solid phase reaction easily proceeds, so that a uniformlight emitting material can be obtained. Furthermore, a high-puritylight emitting element can be obtained since an unnecessary impurityelement is not mixed. As the compound including the first impurityelement and the second impurity element, copper chloride (CuCl), silverchloride (AgCl), or the like can be used, for example.

Note that the concentration of the impurity element to the base materialmay be in the range of 0.01 atomic % to 10 atomic %, preferably 0.05atomic % to 5 atomic %.

As the light emitting material having the light emitting center ofdonor-acceptor recombination light emission, a light emitting materialcontaining a third impurity element may alternatively be used. In thiscase, the concentration of the third impurity element to the basematerial is preferably in the range of 0.05 atomic % to 5 atomic %. Thelight emitting material having such a structure enables light emissionat low voltage. Accordingly, a light emitting element which can emitlight at low drive voltage can be obtained, and a light emitting elementof which power consumption is reduced can be obtained. In addition, animpurity element serving as the above-described light emitting center oflocalized light emission may further be included.

As such a light emitting material, a light emitting material containingZnS as the base material, Cl as the first impurity element, Cu as thesecond impurity element, Ga and As as the third impurity element, and Mnas the light emitting center of localized light emission, can be used.The following method can be used to form such a light emitting material.Mn is added to a light emitting material (ZnS:Cu, Cl), which is baked ina vacuum for two to four hours. The baking temperature is preferably inthe range of 700° C. to 1500° C. This baked material is crushed to aparticle size of 5 μm to 20 μm, GaAs having a particle size of 1 μm to 3μm is added thereto, and the mixture is stirred. The mixture is bakedunder a nitrogen stream including a sulfur gas at approximately 500° C.to 800° C. for two to four hours to obtain a light emitting material. Byforming a thin film using this light emitting material by an evaporationmethod or the like, the thin film can be used as a light emitting layerof a light emitting element.

In the case of the thin-film inorganic EL, the electroluminescent layeris a layer containing the above-described light emitting material, whichcan be formed by a vacuum evaporation method such as a resistanceheating evaporation method or an electron beam evaporation (EBevaporation) method, a physical vapor deposition (PVD) method such as asputtering method, a chemical vapor deposition (CVD) method such as anorganic metal CVD method or a hydride transfer low pressure CVD, anatomic layer epitaxy (ALE) method, or the like.

FIGS. 79A to 79C show examples of a thin-film inorganic EL element whichcan be used as a light emitting element. In FIGS. 79A to 79C, each lightemitting element includes a first electrode layer 50, anelectroluminescent layer 51, and a second electrode layer 53.

Each of the light emitting elements shown in FIGS. 79B and 79C has astructure in which an insulating layer is provided between the electrodelayer and the electroluminescent layer in the light emitting element inFIG. 79A. The light emitting element shown in FIG. 79B includes aninsulating layer 54 between the first electrode layer 50 and theelectroluminescent layer 52. The light emitting element shown in FIG.79C includes an insulating layer 54 a between the first electrode layer50 and the electroluminescent layer 52 and an insulating layer 54 bbetween the second electrode layer 53 and the electroluminescent layer52. As described above; the insulating layer may be provided between theelectroluminescent layer and either or both of the pair of electrodessandwiching the electroluminescent layer. The insulating layer may be asingle layer or a laminate of a plurality of layers.

In FIG. 79B, the insulating layer 54 is provided to be in contact withthe first electrode layer 50. However, the insulating layer 54 may beprovided to be in contact with the second electrode layer 53 byreversing the order of the insulating layer and the electroluminescentlayer.

In the case of the dispersed inorganic EL element, a particulate lightemitting material is dispersed in a binder to form a filmelectroluminescent layer. In the case where a particle having a desiredsize cannot be sufficiently obtained by a production method of a lightemitting material, the material may be processed into particles bycrushing in a mortar or the like. The binder is a substance for fixing aparticulate light emitting material in a dispersed manner and holdingthe material in shape as the electroluminescent layer. The lightemitting material is uniformly dispersed and fixed in theelectroluminescent layer by the binder.

In the case of the dispersed inorganic EL element, theelectroluminescent layer can be, formed by a droplet discharge methodwhich can selectively form the electroluminescent layer, a printingmethod (such as screen printing or off-set printing), a coating methodsuch as a spin-coating method, a dipping method, a dispenser method, orthe like. The thickness is not particularly limited, but it ispreferably in the range of 10 nm to 1000 nm. In addition, in theelectroluminescent layer containing the light emitting material and thebinder, the proportion of the light emitting material is preferably inthe range of 50 wt % to 80 wt %.

FIGS. 80A to 80C show examples of a dispersed inorganic EL element whichcan be used as a light emitting element. A light emitting element inFIG. 80A has a laminated structure of a first electrode layer 60, anelectroluminescent layer 62, and a second electrode layer 63, andcontains a light emitting material 61 held by a binder in theelectroluminescent layer 62.

As the binder which can be used in this embodiment, an insulatingmaterial, an organic material or an inorganic material, or a mixedmaterial of an organic material and an inorganic material can be used.As an organic insulating material, a polymer having a relatively highdielectric constant, such as a cyanoethyl cellulose resin, or a resinsuch as polyethylene, polypropylene, a polystyrene resin, a siliconeresin, an epoxy resin, or vinylidene fluoride can be used.Alternatively, a heat resistant high molecular compound such as aromaticpolyamide or polybenzimidazole, or a siloxane resin may be used. Notethat the siloxane resin corresponds to a resin including a Si—O—Si bond.Siloxane includes a skeleton formed from a bond of silicon (Si) andoxygen (O). An organic group containing at least hydrogen (for example,an alkyl group or aromatic hydrocarbon) or a fluoro group may be usedfor a substituent, or an organic group containing at least hydrogen anda fluoro group may be used for substituents. Alternatively, a resinmaterial such as a vinyl resin of polyvinyl alcohol, polyvinylbutyral,or the like, a phenol resin, a novolac resin, an acrylic resin, amelamine resin, a urethane resin, or an oxazole resin (polybenzoxazole)may be used. In addition, for example, a photo-curing type resin or thelike can be used. A dielectric constant can be adjusted by appropriatelymixing high dielectric constant fine particles such as barium titanate(BaTiO₃) or strontium titanate (SrTiO₃) in the above resin.

As an inorganic insulating material included in the binder, a materialselected from substances containing inorganic insulating materials canbe used, such as silicon oxide (SiO_(X)), silicon nitride (SiN_(X)),silicon containing oxygen and nitrogen, aluminum nitride (AlN), aluminumcontaining oxygen and nitrogen, aluminium oxide (Al₂O₃), titanium oxide(TiO₂), BaTiO₃, SrTiO₃, lead titanate (PbTiO₃), potassium niobate(KNbO₃), lead niobate (PbNbO₃), tantalum oxide (Ta₂O₅), barium tantalate(BaTa₂O₆), lithium tantalate (LiTaO₃), yttrium oxide (Y₂O₃), zirconiumoxide (ZrO₂), or ZnS. A dielectric constant of the electroluminescentlayer including the light emitting material and the binder can becontrolled by making an organic material to contain a high dielectricconstant inorganic material, so that a dielectric constant can beincreased.

In a producing process, a light emitting material is dispersed in asolution including a binder. As a solvent of the solution including thebinder that can be used in this embodiment, a solvent in which a bindermaterial is soluble and which can produce a solution having a viscositysuitable for a method for forming the electroluminescent layer (variouswet processes) and a desired thickness, may be selected appropriately.An organic solvent or the like can be used. In the case of using, forexample, a siloxane resin as the binder, propylene glycol monomethylether, propylene glycol monomethyl ether acetate (also referred to asPGMEA), 3-methoxy-3-methyl-1-butanol (also referred to as MMB), or thelike can be used.

Each of the light emitting elements shown in FIGS. 80B and 80C has astructure in which an insulating layer is provided between the electrodelayer and the electroluminescent layer in the light emitting element inFIG. 80A. The light emitting element shown in FIG. 80B includes aninsulating layer 64 between the first electrode layer 60 and theelectroluminescent layer 62. The light emitting element shown in FIG.80C includes an insulating layer 64 a between the first electrode layer60 and the electroluminescent layer 62 and an insulating layer 64 bbetween the second electrode layer 63 and the electroluminescent layer62. As described above, the insulating layer may be provided between theelectroluminescent layer and either or both of the pair of electrodessandwiching the electroluminescent layer. In addition, the insulatinglayer may be a single layer or a laminate of a plurality of layers.

In FIG. 80B, the insulating layer 64 is provided to be in contact withthe first electrode layer 60. However, the insulating layer 64 may beprovided to be in contact with the second electrode layer 63 byreversing the order of the insulating layer and the electroluminescentlayer.

An insulating layer such as the insulating layer 54 in FIGS. 79A to 79Cor the insulating layer 64 in FIGS. 80A to 80C is not particularlylimited, but it preferably has high insulation resistance and dense filmquality. Furthermore, it preferably has a high dielectric constant. Forexample, a film of silicon oxide (SiO₂), yttrium oxide (Y₂O₃), titaniumoxide (TiO₂), aluminum oxide (Al₂O₃), hafnium oxide (HfO₂), tantalumoxide (Ta₂O₅), barium titanate (BaTiO₃), strontium titanate (SrTiO₃),lead titanate (PbTiO₃), silicon nitride (Si₃N₄), zirconium oxide (ZrO₂),or the like, a mixed film thereof, or a laminated film of two or morekinds can be used. These insulating films can be formed by sputtering,evaporation, CVD, or the like. Alternatively, the insulating layer maybe formed by dispersing particles of the insulating material in abinder. A binder material may be formed using a material and a methodsimilar to those of the binder included in the electroluminescent layer.The thickness is not particularly limited, but it is preferably in therange of 10 nm to 1000 nm.

The light emitting element described in this embodiment, which canprovide light emission by applying voltage between a pair of electrodelayers sandwiching the electroluminescent layer, can be operated byeither DC drive or AC drive.

Note that the light emitting element described in this embodiment can beapplied to the light emitting element of this specification and can beapplied, for example, to the light emitting element of the display panelin Embodiment 2. In that case, the electroluminescent layer of thisembodiment corresponds to the layer 6616 containing an organic compoundof Embodiment 2 shown in FIGS. 66A and 66B.

Embodiment 8

In this embodiment, a structure of a display panel in the case of usinga liquid crystal element as a display element is explained.

FIG. 71A shows a liquid crystal display panel in which a signal linedriver circuit 7130, a scan line driver circuit 7138, and a pixelportion 7131 are formed over a first substrate 7100.

FIG. 71B is a cross-sectional view of the liquid crystal display panelalong a line A-A′, which shows the signal line driver circuit 7130provided with a CMOS circuit including an n-channel TFT 7121 and ap-channel TFT 7122 over the first substrate 7100. The n-channel TFT 7121and the p-channel TFT 7122 may be formed to include a crystallinesemiconductor film. A TFT forming the signal line driver circuit 7130 orthe scan line driver circuit 7138 may be formed with a CMOS circuit, aPMOS circuit, or an NMOS circuit.

The pixel portion 7131 includes a TFT 7123 and a capacitor 7158. The TFT7123 may be formed to include a crystalline semiconductor film. Thecapacitor 7158 includes a semiconductor film to which an impurity isadded and a gate insulating film sandwiched between the semiconductorfilm and a gate electrode.

Note that the TFT 7123 of the pixel portion 7131 does not need to havehigh crystallinity as compared to the signal line driver circuit 7130and the scan line driver circuit 7138.

In addition, the pixel portion 7131 includes a pixel electrode 7111connected to one electrode of the TFT 7123. Then, a third insulatingfilm 7109 is provided so as to cover the n-channel TFT 7121, thep-channel TFT 7122, the pixel electrode 7111, the TFT 7123, and thelike.

Further, a second substrate 7145 serving as an opposite substrate isprepared. The second substrate 7145 is provided with a black matrix 7151in a position corresponding to at least the signal line driver circuit7130, provided with a color filter 7152 in a position corresponding toat least the pixel portion, and further provided with an oppositeelectrode 7153. In the invention, the black matrix, the color filter, orthe opposite electrode is not necessarily provided over the secondsubstrate 7145, and may be provided on the first substrate 7100 side.Thereafter, a spacer 7156 for keeping a substrate interval may beformed. In addition, a projection 7150 for preventing convection of aliquid crystal material in order to prevent distribution bias of organicferroelectric fine particles mixed in a liquid crystal material may beformed simultaneously. As the spacer 7156, a spherical spacer may beused, or a so-called columnar spacer formed by etching an insulatingfilm may be used. Furthermore, the projection 7150 may be formed to havea height equal to the thickness of a liquid crystal layer 7154 so as tohave the same function as the space 7156. Whether both the spacer 7156and the projection 7150 are separately formed or the spacer 7156 issubstituted by the projection 7150, is appropriately selected.

Subsequently, the second substrate 7145 is subjected to orientationtreatment and attached to the first substrate 7100 with a sealant 7143.As the sealant 7143, an epoxy resin is preferably used. In addition,part of the third insulating film 7109 may be left in a position wherethe sealant 7143 is to be formed. As a result, an attachment area isenlarged, and attachment strength can be increased. Note that the spacer7156 for keeping a substrate interval may be formed after performingorientation treatment on an orientation film.

A liquid crystal layer 7154 is injected between the first substrate 7100and the second substrate 7145. The injection of the liquid crystal layer7154 is preferably performed in a vacuum. Alternatively, after droppinga liquid crystal layer onto the first substrate 7100, the secondsubstrate 7145 may be attached. Particularly in the case of using alarge-sized substrate, a liquid crystal layer is preferably droppedrather than being injected.

Furthermore, the first substrate 7100 or the second substrate 7145 maybe appropriately provided with a polarizing plate or a circularlypolarizing plate to enhance contrast.

A flexible printed circuit (FPC) 7146 is connected to a conductive film7108 provided in a first attachment region 7132 with an anisotropicconductive film (ACF). Then, a video signal and a clock signal which areexternal input signals are supplied through the FPC 7146. Note that onlythe FPC is shown here; however, a printed wiring board (PWB) is attachedthrough this FPC. In addition, an external signal generation circuit ismounted on the printed wiring board.

In attaching the ACF by pressurization or heating, attention needs to bepaid so as to prevent a crack from generating due to flexibility of thesubstrate or softening by heating. For example, a substrate having highrigidity may be provided at least below the first attachment region7132.

In this embodiment, a driver-integrated type light emitting deviceprovided with the signal line driver circuit 7130 and the scan linedriver circuit 7138 over the first substrate 7100 is described. However,the signal line driver circuit and the scan line driver circuit may beformed with ICs and may be connected to a signal line, a scan line, orthe like by a SOG method or a TAB method.

As described above, the liquid crystal display panel can bemanufactured.

This application is based on Japanese Patent Application serial no.2005-133741 filed in Japan Patent Office on Apr. 28, 2005, the entirecontents of which are hereby incorporated by reference.

1-15. (canceled)
 16. A display device comprising: a pixel portionincluding a plurality of transistors, wherein each of the plurality oftransistors contains InGaZnO in a channel formation region; a drivercircuit portion including a latch circuit and a shift register; and aconnection terminal portion, wherein the connection terminal portionincludes a plurality of connection terminals, wherein the plurality ofconnection terminals are provided with a plurality of connection pads,each of which is part of the connection terminal, wherein the pluralityof connection pads include a first connection pad and a secondconnection pad having a line width different from that of the firstconnection pad, wherein a plurality of wires are electrically connectedto the second connection pad, wherein the plurality of wires areelectrically connected to an opposite electrode, and wherein theopposite electrode overlaps the shift register and does not overlap thelatch circuit.
 17. A display device according to claim 16, wherein aflexible printed circuit is connected to the connection terminalportion.
 18. A display device according to claim 17, wherein at leastone connection terminal in the connection terminal portion is connectedto a plurality of terminals of the flexible printed circuit, and acontact resistance between the connection terminal and the plurality ofterminals of the flexible printed circuit is 5Ω or less.
 19. A displaydevice according to claim 16, wherein the display device is incorporatedin at least one selected from the group consisting of a camera, acomputer, a mobile computer, a goggle type display, a video camera, animage reproducing device, and a mobile phone.
 20. A display devicecomprising: a pixel portion including a plurality of transistors,wherein each of the plurality of transistors contains InGaZnO in achannel formation region; a driver circuit portion including a latchcircuit and a shift register; and a connection terminal portion, whereinthe connection terminal portion includes a plurality of connectionterminals, wherein the plurality of connection terminals are providedwith a plurality of connection pads, each of which is part of theconnection terminal, wherein the plurality of connection pads include afirst connection pad and a second connection pad having a line widthdifferent from that of the first connection pad, wherein pitches betweenthe plurality of connection pads are equal to each other, wherein aplurality of wires are electrically connected to the second connectionpad, wherein the plurality of wires are electrically connected to anopposite electrode, and wherein the opposite electrode overlaps theshift register and does not overlap the latch circuit.
 21. A displaydevice according to claim 20, wherein a flexible printed circuit isconnected to the connection terminal portion.
 22. A display deviceaccording to claim 21, wherein at least one connection terminal in theconnection terminal portion is connected to a plurality of terminals ofthe flexible printed circuit, and a contact resistance between theconnection terminal and the plurality of terminals of the flexibleprinted circuit is 5Ω or less.
 23. A display device according to claim20, wherein the display device is incorporated in at least one selectedfrom the group consisting of a camera, a computer, a mobile computer, agoggle type display, a video camera, an image reproducing device, and amobile phone.
 24. A display device comprising: a pixel portion includinga plurality of transistors, wherein each of the plurality of transistorscontains InGaZnO in a channel formation region; a driver circuit portionincluding a latch circuit and a shift register; and a connectionterminal portion, wherein the connection terminal portion includes aplurality of connection terminals, wherein the plurality of connectionterminals are provided with a plurality of connection pads, each ofwhich is part of the connection terminal, wherein pitches between theplurality of connection pads are equal to each other, wherein theplurality of connection pads include a first connection pad and a secondconnection pad having a line width larger than that of the firstconnection pad, wherein a plurality of wires are electrically connectedto the second connection pad, wherein the plurality of wires areelectrically connected to an opposite electrode, and wherein theopposite electrode overlaps the shift register and does not overlap thelatch circuit.
 25. A display device according to claim 24, wherein thedisplay device is incorporated in at least one selected from the groupconsisting of a camera, a computer, a mobile computer, a goggle typedisplay, a video camera, an image reproducing device, and a mobilephone.